Perhapsatron
Encyclopedia
The Perhapsatron was an early fusion power
device based on the pinch
concept. Dreamt up by James (Jim) Tuck while working at Los Alamos National Laboratory
(LANL), he named the device whimsically on the off chance that it might be able to create fusion reactions.
The first example was built in the winter of 1952/53, and quickly demonstrated a series of instabilities in the plasma
that plagued the pinch concept. A series of modifications followed that attempted to correct these problems, leading to the ultimate "S-4" model, but none of these proved fruitful and most work on the pinch concept ended around 1961.
Capturing that energy on a smaller industrial scale would not be easy - plasma at that temperature would melt any physical container. As plasma is electrically conductive it was obvious that it could be contained magnetically, but the proper arrangement of the fields was not obvious -- Fermi pointed out that a simple toroid would cause the fuel to drift out of the "bottle". Several arrangements were eventually studied over time, notably the stellarator
concept developed around 1950.
An alternate approach was the "pinch" concept, developed in the United Kingdom
. Unlike the magnetic bottle approaches, in a pinch device the required magnetic field was created by the plasma itself. Since the plasma is electrically conductive, if one runs a current through the plasma it would create an induced magnetic field. According to Lenz's law
, this field would be arranged in a way to resist the flow of the current. This field, through the Lorentz force
, will act to compress the conductor. In the case of a plasma, the force would collapse it into a thin filament, "pinching" it down. Since the current had to be very large, pinch devices made no attempt to confine the plasmas for extended periods, they would attempt to reach fusion conditions quickly and then extract power from the resulting hot products.
The pinch concept was patented in 1946 by George Paget Thomson
and Moses Blackman
, who explored both linear and toroidal pinch machines. Jim Tuck was first introduced to these concepts in January 1947 at a meeting arranged at the Atomic Energy Research Establishment, Harwell
. Tuck studied the Thompson-Blackman work and concluded that they would not reach fusion condition, but would nevertheless be interesting as an experimental system. Working at the Clarendon Laboratory
at Oxford University, he arranged funding for an experimental device and started assembling it. Before it was complete he was lured to the US by a job offer at the University of Chicago
.
Other teams in the UK continued their efforts. Thomson passed his concepts on to Stan Cousins and Alan Ware, who assembled a linear pinch device out of old radar equipment and started operations in 1947. Follow-on experiments used large banks of capacitor
s to store energy that was quickly dumped into the plasma through a solenoid
wrapped around a short tube. These experiments demonstrated a number of dynamic instabilities that caused the plasma to break up and hit the walls of the tube long before it was compressed or heated enough to reach the required fusion conditions.
of the deuterium
-tritium
fusion reaction. This work continued to pique his interest in fusion power, and he spent some time through 1951 considering the problem.
At Los Alamos, Tuck acquainted the US researchers with the British efforts. By this point Lyman Spitzer
had introduced his stellarator
concept and was shopping the idea around the energy establishment looking for funding. In 1951 he approached the U.S. Atomic Energy Commission (AEC) to fund his design. Tuck was skeptical of Spitzer's enthusiasm and felt his aggressive development program was "incredibly ambitious", and proposed a much less aggressive program based on pinch. Both men presented their ideas in Washington in May 1951. In July, Spitzer received $50,000 and Tuck was sent away empty handed. Not to be outdone, Tuck convinced Norris Bradbury
, the Los Alamos director, to give him $50,000 from the discretionary budget, using it to build the Perhapsatron
.
Still unconvinced that the concept would work on the first attempt, he called this approach, with Stanislaw Ulam's input, the Perhapsatron. Tuck put together a small team and used scrounged parts to build the first Perhapsatron, built in 1952/53. The Perhapsatron used a toroidal tube made in the local glass shop. Sitting in the middle of the toroid was a large iron core from a transformer
, which was used to induce the current into the gas.
The Perhapsatron quickly displayed the same problems as the British experiments. No matter how slowly the current was added, once it reached a critical point the instabilities always arose. In 1954, Martin David Kruskal and Martin Schwarzschild
published a critical paper on the issue, which suggested that all Z-pinch devices were inherently unstable. Tuck then proposed the addition of a second, steady, magnetic field running longitudinal along the tube, a concept he called "adding a backbone to the plasma". Several modifications to the Perhapsatron followed to test variations on these concepts, but none of these proved fruitful.
Tuck was never married to the pinch concept, and spent considerable effort on other concepts - which led to joking within Los Alamos about his apparently unfocused work. Over the years he led development of several other concepts, including the picket-fence reactor, new pinch concepts, and work on mainstream devices.
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...
device based on the pinch
Pinch (plasma physics)
A pinch is the compression of an electrically conducting filament by magnetic forces. The conductor is usually a plasma, but could also be a solid or liquid metal...
concept. Dreamt up by James (Jim) Tuck while working at Los Alamos National Laboratory
Los Alamos National Laboratory
Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...
(LANL), he named the device whimsically on the off chance that it might be able to create fusion reactions.
The first example was built in the winter of 1952/53, and quickly demonstrated a series of instabilities in the 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...
that plagued the pinch concept. A series of modifications followed that attempted to correct these problems, leading to the ultimate "S-4" model, but none of these proved fruitful and most work on the pinch concept ended around 1961.
Early fusion efforts
Scientists at Los Alamos had a long history studying nuclear fusion, and by 1946 had already calculated that a steady-state plasma would have to be heated to 100 million degrees Celsius in order to "ignite" and release net energy. This was of vital interest in the nuclear bomb establishment, where the use of a small atomic bomb "trigger" was used to provide the required temperatures.Capturing that energy on a smaller industrial scale would not be easy - plasma at that temperature would melt any physical container. As plasma is electrically conductive it was obvious that it could be contained magnetically, but the proper arrangement of the fields was not obvious -- Fermi pointed out that a simple toroid would cause the fuel to drift out of the "bottle". Several arrangements were eventually studied over time, notably the stellarator
Stellarator
A stellarator is a device used to confine a hot plasma with magnetic fields in order to sustain a controlled nuclear fusion reaction. It is one of the earliest controlled fusion devices, first invented by Lyman Spitzer in 1950 and built the next year at what later became the Princeton Plasma...
concept developed around 1950.
Z-pinch
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
. Unlike the magnetic bottle approaches, in a pinch device the required magnetic field was created by the plasma itself. Since the plasma is electrically conductive, if one runs a current through the plasma it would create an induced magnetic field. According to Lenz's law
Lenz's law
Lenz's law is a common way of understanding how electromagnetic circuits must always obey Newton's third law and The Law of Conservation of Energy...
, this field would be arranged in a way to resist the flow of the current. This field, through the Lorentz force
Lorentz force
In physics, the Lorentz force is the force on a point charge due to electromagnetic fields. It is given by the following equation in terms of the electric and magnetic fields:...
, will act to compress the conductor. In the case of a plasma, the force would collapse it into a thin filament, "pinching" it down. Since the current had to be very large, pinch devices made no attempt to confine the plasmas for extended periods, they would attempt to reach fusion conditions quickly and then extract power from the resulting hot products.
The pinch concept was patented in 1946 by George Paget Thomson
George Paget Thomson
Sir George Paget Thomson, FRS was an English physicist and Nobel laureate in physics recognised for his discovery with Clinton Davisson of the wave properties of the electron by electron diffraction.-Biography:...
and Moses Blackman
Moses Blackman
Moses Blackman was a South African-born British crystallographer.His father was a minister of religion, Rev. Joseph Blackman.-Education:...
, who explored both linear and toroidal pinch machines. Jim Tuck was first introduced to these concepts in January 1947 at a meeting arranged at the Atomic Energy Research Establishment, Harwell
Atomic Energy Research Establishment
The Atomic Energy Research Establishment near Harwell, Oxfordshire, was the main centre for atomic energy research and development in the United Kingdom from the 1940s to the 1990s.-Founding:...
. Tuck studied the Thompson-Blackman work and concluded that they would not reach fusion condition, but would nevertheless be interesting as an experimental system. Working at the Clarendon Laboratory
Clarendon Laboratory
The Clarendon Laboratory, located on Parks Road with the Science Area in Oxford, England , is part of the Physics Department at Oxford University...
at Oxford University, he arranged funding for an experimental device and started assembling it. Before it was complete he was lured to the US by a job offer at the University of Chicago
University of Chicago
The University of Chicago is a private research university in Chicago, Illinois, USA. It was founded by the American Baptist Education Society with a donation from oil magnate and philanthropist John D. Rockefeller and incorporated in 1890...
.
Other teams in the UK continued their efforts. Thomson passed his concepts on to Stan Cousins and Alan Ware, who assembled a linear pinch device out of old radar equipment and started operations in 1947. Follow-on experiments used large banks of capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
s to store energy that was quickly dumped into the plasma through a solenoid
Solenoid
A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...
wrapped around a short tube. These experiments demonstrated a number of dynamic instabilities that caused the plasma to break up and hit the walls of the tube long before it was compressed or heated enough to reach the required fusion conditions.
Perhapsatron
After a short time in Chicago, Tuck was hired by Los Alamos to work on the "Super" project, the hydrogen bomb., where he was put on the task of calculating the nuclear cross sectionNuclear cross section
The nuclear cross section of a nucleus is used to characterize the probability that a nuclear reaction will occur. The concept of a nuclear cross section can be quantified physically in terms of "characteristic area" where a larger area means a larger probability of interaction...
of the 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 ...
-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...
fusion reaction. This work continued to pique his interest in fusion power, and he spent some time through 1951 considering the problem.
At Los Alamos, Tuck acquainted the US researchers with the British efforts. By this point Lyman Spitzer
Lyman Spitzer
Lyman Strong Spitzer, Jr. was an American theoretical physicist and astronomer best known for his research in star formation, plasma physics, and in 1946, for conceiving the idea of telescopes operating in outer space...
had introduced his stellarator
Stellarator
A stellarator is a device used to confine a hot plasma with magnetic fields in order to sustain a controlled nuclear fusion reaction. It is one of the earliest controlled fusion devices, first invented by Lyman Spitzer in 1950 and built the next year at what later became the Princeton Plasma...
concept and was shopping the idea around the energy establishment looking for funding. In 1951 he approached the U.S. Atomic Energy Commission (AEC) to fund his design. Tuck was skeptical of Spitzer's enthusiasm and felt his aggressive development program was "incredibly ambitious", and proposed a much less aggressive program based on pinch. Both men presented their ideas in Washington in May 1951. In July, Spitzer received $50,000 and Tuck was sent away empty handed. Not to be outdone, Tuck convinced Norris Bradbury
Norris Bradbury
Norris Edwin Bradbury , was an American physicist who was born in Santa Barbara, California. He served as director of the Los Alamos National Laboratory for 25 years , succeeding J. Robert Oppenheimer, who personally chose Bradbury for the position of director after working closely with him on the...
, the Los Alamos director, to give him $50,000 from the discretionary budget, using it to build the Perhapsatron
Perhapsatron
The Perhapsatron was an early fusion power device based on the pinch concept. Dreamt up by James Tuck while working at Los Alamos National Laboratory , he named the device whimsically on the off chance that it might be able to create fusion reactions.The first example was built in the winter of...
.
Still unconvinced that the concept would work on the first attempt, he called this approach, with Stanislaw Ulam's input, the Perhapsatron. Tuck put together a small team and used scrounged parts to build the first Perhapsatron, built in 1952/53. The Perhapsatron used a toroidal tube made in the local glass shop. Sitting in the middle of the toroid was a large iron core from a transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
, which was used to induce the current into the gas.
The Perhapsatron quickly displayed the same problems as the British experiments. No matter how slowly the current was added, once it reached a critical point the instabilities always arose. In 1954, Martin David Kruskal and Martin Schwarzschild
Martin Schwarzschild
Martin Schwarzschild was a German American astronomer. He was the son of famed astrophysicist Karl Schwarzschild and the nephew of the Swiss astrophysicist Robert Emden.-Biography:...
published a critical paper on the issue, which suggested that all Z-pinch devices were inherently unstable. Tuck then proposed the addition of a second, steady, magnetic field running longitudinal along the tube, a concept he called "adding a backbone to the plasma". Several modifications to the Perhapsatron followed to test variations on these concepts, but none of these proved fruitful.
Z-pinch goes out of favor
The failure of Perhapsatron was followed by the failure of other pinch devices. Another team at Los Alamos had been working on another fast-pinch machine that used electrical fields instead of magnetic, known as Columbus, with the same results. Meanwhile the much larger ZETA machine in the UK also failed, but only after publishing results with great fanfare saying they had successfully achieved fusion. By 1961 work on Z-pinch devices had largely ended, although some research continued on the related theta-pinch concept.Tuck was never married to the pinch concept, and spent considerable effort on other concepts - which led to joking within Los Alamos about his apparently unfocused work. Over the years he led development of several other concepts, including the picket-fence reactor, new pinch concepts, and work on mainstream devices.