![Z-pinch H-gamma](https://upload.wikimedia.org/wikipedia/commons/d/db/Z-pinch_H-gamma.jpg)
In
fusion power
Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion, nuclear fusion reactions. In a fusion process, two lighter atomic nucleus, atomic nuclei combine to form a heavier nucleus, whi ...
research, the Z-pinch (zeta pinch) is a type of
plasma
Plasma or plasm may refer to:
Science
* Plasma (physics), one of the four fundamental states of matter
* Plasma (mineral), a green translucent silica mineral
* Quark–gluon plasma, a state of matter in quantum chromodynamics
Biology
* Blood pla ...
confinement system that uses an electric current in the plasma to generate a magnetic field that compresses it (see
pinch). These systems were originally referred to simply as pinch or Bennett pinch (after
Willard Harrison Bennett
Willard Harrison Bennett (June 13, 1903 – September 28, 1987) was an American scientist and inventor, born in Findlay, Ohio. Bennett conducted research into plasma physics, astrophysics, geophysics, surface physics, and physical chemistry. ...
), but the introduction of the
θ-pinch (theta pinch) concept led to the need for clearer, more precise terminology.
The name refers to the direction of the current in the devices, the Z-axis on a normal
three-dimensional graph A three-dimensional graph may refer to
* A graph (discrete mathematics), embedded into a three-dimensional space
* The graph of a function of two variables
In mathematics, the graph of a function f is the set of ordered pairs (x, y), where f(x ...
. Any machine that causes a pinch effect due to current running in that direction is correctly referred to as a Z-pinch system, and this encompasses a wide variety of devices used for an equally wide variety of purposes. Early uses focused on fusion research in donut-shaped tubes with the Z-axis running down the inside the tube, while modern devices are generally cylindrical and used to generate high-intensity
x-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
sources for the study of
nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bom ...
s and other roles. It is one of the first approaches to
fusion power
Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion, nuclear fusion reactions. In a fusion process, two lighter atomic nucleus, atomic nuclei combine to form a heavier nucleus, whi ...
devices, along with the
stellarator
A stellarator is a plasma device that relies primarily on external magnets to confine a plasma. Scientists researching magnetic confinement fusion aim to use stellarator devices as a vessel for nuclear fusion reactions. The name refers to the ...
and
magnetic mirror
A magnetic mirror, known as a magnetic trap (магнитный захват) in Russia and briefly as a pyrotron in the US, is a type of magnetic confinement device used in fusion power to trap high temperature plasma using magnetic fields. T ...
.
Physics
The Z-pinch is an application of the
Lorentz force
In physics (specifically in electromagnetism) the Lorentz force (or electromagnetic force) is the combination of electric and magnetic force on a point charge due to electromagnetic fields. A particle of charge moving with a velocity in an elect ...
, in which a current-carrying conductor in a magnetic field experiences a force. One example of the Lorentz force is that, if two parallel wires are carrying current in the same direction, the wires will be pulled toward each other. In a Z-pinch machine the wires are replaced by a
plasma
Plasma or plasm may refer to:
Science
* Plasma (physics), one of the four fundamental states of matter
* Plasma (mineral), a green translucent silica mineral
* Quark–gluon plasma, a state of matter in quantum chromodynamics
Biology
* Blood pla ...
, which can be thought of as many current-carrying wires. When a current is run through the plasma, the particles in the plasma are pulled toward each other by the Lorentz force, thus the plasma contracts. The contraction is counteracted by the increasing gas pressure of the plasma.
As the plasma is electrically conductive, a magnetic field nearby will induce a current in it. This provides a way to run a current into the plasma without physical contact, which is important as a plasma can rapidly erode mechanical
electrodes
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...
. In practical devices this was normally arranged by placing the plasma vessel inside the core of a
transformer
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
, arranged so the plasma itself would be the secondary. When current was sent into the primary side of the transformer, the magnetic field induced a current into the plasma. As induction requires a ''changing'' magnetic field, and the induced current is supposed to run in a single direction in most reactor designs, the current in the transformer has to be increased over time to produce the varying magnetic field. This places a limit on the product of confinement time and magnetic field, for any given source of power.
In Z-pinch machines the current is generally provided from a large bank of
capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of ...
s and triggered by a
spark gap
A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential difference between the conduct ...
, known as a Marx Bank or
Marx generator
A Marx generator is an electrical circuit first described by Erwin Otto Marx in 1924. Its purpose is to generate a high-voltage pulse from a low-voltage DC supply. Marx generators are used in high-energy physics experiments, as well as to simulat ...
. As the conductivity of plasma is fairly good, about that of
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
, the energy stored in the power source is quickly depleted by running through the plasma. Z-pinch devices are inherently pulsed in nature.
History
Early machines
![Kink instability at Aldermaston](https://upload.wikimedia.org/wikipedia/commons/9/9b/Kink_instability_at_Aldermaston.jpg)
Pinch devices were among the earliest efforts in fusion power. Research began in the UK in the immediate post-war era, but a lack of interest led to little development until the 1950s. The announcement of the
Huemul Project
The Huemul Project ( es, Proyecto Huemul) was an early 1950s Argentine effort to develop a fusion power device known as the Thermotron. The concept was invented by Austrian scientist Ronald Richter, who claimed to have a design that would produce ...
in early 1951 led to fusion efforts around the world, notably in the UK and in the US (see
Perhapsatron The Perhapsatron was an early fusion power device based on the pinch concept in the 1950s. Conceived by James (Jim) Tuck while working at Los Alamos National Laboratory (LANL), he whimsically named the device on the chance that it might be able to ...
, a z-pinch machine at
LANL
Los Alamos National Laboratory (often shortened as Los Alamos and LANL) is one of the sixteen research and development laboratories of the United States Department of Energy (DOE), located a short distance northwest of Santa Fe, New Mexico, ...
). Small experiments were built at labs as various practical issues were addressed, but all of these machines demonstrated unexpected instabilities of the plasma that would cause it to hit the walls of the container vessel. The problem became known as the "
kink instability
A kink instability (also kink oscillation or kink mode), is a current-driven plasma instability characterized by transverse displacements of a plasma column's cross-section from its center of mass without any change in the characteristics of the p ...
".
Stabilized pinch
By 1953 the "stabilized pinch" seemed to solve the problems encountered on earlier devices. Stabilized pinch machines added external magnets that created a toroidal magnetic field inside the chamber. When the device was fired, this field added to the one created by the current in the plasma. The result was that the formerly straight magnetic field was twisted into a helix, which the particles followed as they traveled around the tube driven by the current. A particle near the outside of the tube that wanted to kink outward would travel along these lines until it returned to the inside of the tube, where its outward-directed motion would bring it back into the centre of the plasma.
Researchers in the UK started construction of
ZETA
Zeta (, ; uppercase Ζ, lowercase ζ; grc, ζῆτα, el, ζήτα, label= Demotic Greek, classical or ''zē̂ta''; ''zíta'') is the sixth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 7. It was derived f ...
in 1954. ZETA was by far the largest fusion device of its era. At the time, almost all fusion research was classified, so progress on ZETA was generally unknown outside the labs working on it. However US researchers visited ZETA and realized that they were about to be outpaced. Teams on both sides of the Atlantic rushed to be the first to complete stabilized pinch machines.
ZETA won the race, and by the summer of 1957 it was producing bursts of
neutron
The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
s on every run. Despite the researchers' reservations, their results were released with great fanfare as the first successful step on the path to commercial fusion energy. However, further study soon demonstrated that the measurements were misleading, and none of the machines were near fusion levels. Interest in pinch devices faded, although ZETA and its cousin
Sceptre
A sceptre is a staff or wand held in the hand by a ruling monarch as an item of royal or imperial insignia. Figuratively, it means royal or imperial authority or sovereignty.
Antiquity
Ancient Egypt and Mesopotamia
The ''Was'' and other ...
served for many years as experimental devices.
Fusion-based propulsion
A concept of Z-pinch fusion propulsion system was developed through collaboration between
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
and private companies. The energy released by the Z-pinch effect would accelerate lithium propellant to a high speed, resulting in a
specific impulse
Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine (a rocket using propellant or a jet engine using fuel) creates thrust. For engines whose reaction mass is only the fuel they carry, specific impulse i ...
value of 19400 s and
thrust
Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that syst ...
of 38 kN. A magnetic nozzle would be required to convert the released energy into a useful impulse. This propulsion method could potentially reduce interplanetary travel times. For example, a mission to Mars would take about 35 days one-way with a total burn time of 20 days and a burned propellant mass of 350 tonnes.
Tokamak
Although it remained relatively unknown for years, Soviet scientists used the pinch concept to develop the
tokamak
A tokamak (; russian: токамáк; otk, 𐱃𐰸𐰢𐰴, Toḳamaḳ) is a device which uses a powerful magnetic field to confine plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being d ...
device. Unlike the stabilized pinch devices in the US and UK, the tokamak used considerably more energy in the stabilizing magnets, and much less in the plasma current. This reduced the instabilities due to the large currents in the plasma, and led to great improvements in stability. The results were so dramatic that other researchers were skeptical when they were first announced in 1968. Members of the still-operational ZETA team were called in to verify the results. The tokamak became the most studied approach to controlled fusion.
Sheared-flow stabilized
Sheared-flow stabilizing uses one or more high speed annular flowing plasma sheaths, surrounding a plasma filament, to stabilize the filament against kink and pinch instabilities.
In 2018, a sheared-flow stabilized Z-pinch demonstrated neutron generation. It was built by a fusion company, Zap Energy, Inc., a spin-out from the
University of Washington
The University of Washington (UW, simply Washington, or informally U-Dub) is a public research university in Seattle, Washington.
Founded in 1861, Washington is one of the oldest universities on the West Coast; it was established in Seattle a ...
, and funded by strategic and financial investors and grants from the Advanced Research Projects Agency – Energy (ARPA–E). Flow stabilized plasma remained stable 5,000 times longer than a static plasma. A mix of 20% deuterium and 80% hydrogen by pressure, produced neutron emissions lasting approximately 5 μs with pinch currents of approximately 200 kA during an approximately 16 μs period of plasma quiescence. Average neutron yield was estimated to be (1.25±0.45)×10
5 neutrons/pulse. Plasma temperatures of 1–2 keV (12–24 million °C) and densities of approximately 10
17 cm
−3 with 0.3 cm pinch radii were measured.
Experiments
![Pinchseta](https://upload.wikimedia.org/wikipedia/commons/9/91/Pinchseta.JPG)
Z-pinch machines can be found at
University of Nevada, Reno
The University of Nevada, Reno (Nevada, the University of Nevada, or UNR) is a public land-grant research university in Reno, Nevada. It is the state's flagship public university and primary land grant institution. It was founded on October 12, ...
(USA),
Cornell University
Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to teach an ...
(USA),
University of Michigan
, mottoeng = "Arts, Knowledge, Truth"
, former_names = Catholepistemiad, or University of Michigania (1817–1821)
, budget = $10.3 billion (2021)
, endowment = $17 billion (2021)As o ...
(USA),
Sandia National Laboratories
Sandia National Laboratories (SNL), also known as Sandia, is one of three research and development laboratories of the United States Department of Energy's National Nuclear Security Administration (NNSA). Headquartered in Kirtland Air Force Ba ...
(USA),
University of California, San Diego
The University of California, San Diego (UC San Diego or colloquially, UCSD) is a public university, public Land-grant university, land-grant research university in San Diego, California. Established in 1960 near the pre-existing Scripps Insti ...
(USA),
University of Washington
The University of Washington (UW, simply Washington, or informally U-Dub) is a public research university in Seattle, Washington.
Founded in 1861, Washington is one of the oldest universities on the West Coast; it was established in Seattle a ...
(USA),
Ruhr University
The Ruhr University Bochum (, ) is a public research university located in the southern hills of the central Ruhr area, Bochum, Germany. It was founded in 1962 as the first new public university in Germany after World War II. Instruction began in ...
(Germany),
Imperial College
Imperial College London (legally Imperial College of Science, Technology and Medicine) is a public research university in London, United Kingdom. Its history began with Prince Albert, consort of Queen Victoria, who developed his vision for a cu ...
(United Kingdom),
École Polytechnique
École may refer to:
* an elementary school in the French educational stages normally followed by secondary education establishments (collège and lycée)
* École (river), a tributary of the Seine flowing in région Île-de-France
* École, Savoi ...
(France),
Weizmann Institute of Science
The Weizmann Institute of Science ( he, מכון ויצמן למדע ''Machon Vaitzman LeMada'') is a public research university in Rehovot, Israel, established in 1934, 14 years before the State of Israel. It differs from other Israeli unive ...
(Israel),
Universidad Autónoma Metropolitana
The Metropolitan Autonomous University (Spanish language, Spanish: ''Universidad Autónoma Metropolitana'') also known as UAM, is a Mexican public university. Founded in 1974 with the support of then-President Luis Echeverria Alvarez, the institut ...
(Mexico), NSTRI (Iran).
See also
*
Z Pulsed Power Facility
The Z Pulsed Power Facility, informally known as the Z machine or Z, is the largest high frequency electromagnetic wave generator in the world and is designed to test materials in conditions of extreme temperature and pressure. It was original ...
*
Pinch (plasma physics)
A pinch (or: Bennett pinch (after Willard Harrison Bennett), electromagnetic pinch, magnetic pinch, pinch effect, or plasma pinch.) is the compression of an electrically conducting Electrical filament, filament by magnetic forces, or a device tha ...
References
External links
Z Machine(Sandia Labs)
An Inertial-Fusion Z-Pinch Power Plant Concept(Sandia Labs)
Development path for Z-pinch IFE"Physics of 'Ocean's Eleven'"The MAGPIE project at Imperial College Londonis used to study wire array Z-pinch implosions.
{{Fusion power
Magnetic confinement fusion
English inventions