Dense plasma focus
Encyclopedia
A dense plasma focus is a machine that produces, by electromagnetic
acceleration and compression, a short-lived plasma
that is so hot and dense that it can cause nuclear fusion
and emit X-rays. The electromagnetic compression of the plasma is called a pinch
. It was invented in the early 1960s by J.W. Mather and also independently by N.V. Filippov. The plasma focus is similar to the high-intensity plasma gun device (HIPGD) (or just plasma gun), which ejects plasma in the form of a plasmoid
, without pinching it.
s and charged particles are emitted, as are nuclear fusion
neutron
s, when operated in deuterium
. There is ongoing research that demonstrates potential applications as a soft X-ray source for next-generation microelectronics
lithography
, surface micromachining
, pulsed X-ray and neutron
source for medical and security inspection applications and materials modification, among others.
For nuclear weapons applications, dense plasma focus devices can be used as an external neutron source
. Other applications include simulation of nuclear explosions (for testing of the electronic equipment) and a short and intense neutron source useful for non-contact discovery or inspection of nuclear materials (uranium, plutonium).
of the focused plasma is practically a constant over the whole range of machines, from sub-kilojoule machines to megajoule machines, when these machines are tuned for optimal operation. This means that a small table-top-sized plasma focus machine produces essentially the same plasma characteristics (temperature and density) as the largest plasma focus. Of course the larger machine will produce the larger volume of focused plasma with a corresponding longer lifetime and more radiation yield.
Even the smallest plasma focus has essentially the same dynamic characteristics as larger machines, producing the same plasma characteristics and the same radiation products. This is due to the scalability of plasma
phenomena.
See also plasmoid
, the self-contained magnetic plasma ball that may be produced by a dense plasma focus.
) is switched onto the anode. The gas breaks down. A rapidly rising electric current
flows across the backwall electrical insulator, axisymmetrically, as depicted by the path (labeled 1) as shown in the fig. 1. The axisymmetric sheath of plasma current lifts off the insulator due to the interaction of the current with its own magnetic field (Lorentz force
). The plasma sheath is accelerated axially, to position 2, and then to position 3, ending the axial phase of the device.
The whole process proceeds at many times the speed of sound
in the ambient gas. As the current sheath continues to move axially, the portion in contact with the anode slides across the face of the anode, axisymmetrically. When the imploding front of the shock wave
coalesces onto the axis, a reflected shock front emanates from the axis until it meets the driving current sheath which then forms the axisymmetric boundary of the pinched, or focused, hot plasma column.
The dense plasma column (akin to the Z-pinch
) rapidly pinch
es and undergoes instabilities and breaks up. The intense electromagnetic and particle bursts, collectively referred to as multi-radiation occur during the dense plasma and breakup phases. These critical phases last typically tens of nanoseconds for a small (kJ, 100 kA) focus to around a microsecond
for a large (MJ, several MA) focus.
The whole process, including axial and radial phases, may last, for the Mather DPF, a few microseconds (for a small focus) to 10 microseconds (for a large focus). A Filippov focus has a very short axial phase compared to a Mather focus.
, or the current linear density divided by the square root of the mass density of the fill gas.
For example for neutron-optimised operation in deuterium the value of this critical parameter, experimentally observed over a range of machines from kilojoules to hundreds of kilojoules, is: 9 A/(m·Torr0.5), or 780 kA/(m·Pa0.5), with a remarkably small deviation of 10% over such a large range of sizes of machines.
Thus if we have a peak current of 180 kA we require an anode radius of 10 mm with a deuterium fill pressure of 4 Torr (533.3 Pa). The length of the anode has then to be matched to the risetime of the capacitor current in order to allow an average axial transit speed of the current sheath of just over 50 mm/μs. Thus a capacitor risetime of 3 μs requires a matched anode length of 160 mm.
The above example of peak current of 180 kA rising in 3 µs, anode radius and length of respectively 10 and 160 mm are close to the design parameters of the UNU/ICTP PFF (United Nations University/International Centre for Theoretical Physics Plasma Fusion Facility). This small table-top device was designed as a low-cost integrated experimental system for training and transfer to initiate/strengthen experimental plasma research in developing countries.
The International Centre for Dense Magnetised Plasmas (ICDMP) in Warsaw Poland, operates several plasma focus machines for an international research and training programme. Among these machines is one with energy capacity of 1 MJ making it one of the largest plasma focus devices in the world.
In Argentina there is an Inter-institutional Program for Plasma Focus Research since 1996, coordinated by a National Laboratory of Dense Magnetized Plasmas (www.pladema.net) in Tandil, Buenos Aires. The Program also cooperates with the Chilean Nuclear Energy Commission, and networks the Argentine National Energy Commission, the Scientific Council of Buenos Aires, the University of Center, the University of Mar del Plata, The University of Rosario, and the Institute of Plasma Physics of the University of Buenos Aires. The program operates six Plasma Focus Devices, developing applications, in particular ultrashort tomography and substance detection by neutron pulsed interrogation. Chile currently operates the facility SPEED-2, the largest Plasma Focus facility of the southern hemisphere. PLADEMA also contributed during the last decade with several mathematical models of Plasma Focus. The thermodynamic model was able to develop for the first time design maps combining geometrical and operational parameters, showing that there is always an optimum gun length and charging pressure which maximize the neutronic emissions. Currently there is a complete finite-elements code validated against numerous experiments, which can be used confidently as a design tool for Plasma Focus.
based on the DPF could be viable, possibly even with low-neutron fuel cycles
like p-B11. The feasibility of net power from p-B11 in the DPF requires that the bremsstrahlung
losses be reduced by quantum mechanical effects induced by the powerful magnetic field. The high magnetic field will also result in a high rate of emission of cyclotron radiation
, but at the densities envisioned, where the plasma frequency is larger than the cyclotron frequency, most of this power will be reabsorbed before being lost from the plasma. Another advantage claimed is the capability of direct conversion of the energy of the fusion products into electricity, with an efficiency potentially above 70%. Experiments and computer simulations to investigate the capability of DPF for fusion power are underway at Lawrenceville Plasma Physics (LPP) under the direction of Eric Lerner
, who explained his "Focus Fusion" approach in a 2007 Google Tech Talk. On November 14, 2008, Lerner received funding for continued research, to test the scientific feasibility of Focus Fusion. On October 15, 2009, the DPF device "Focus Fusion-1" achieved its first pinch. On January 28th, 2011, LPP published initial results including experimental shots with considerably higher fusion yields than the historical DPF trend.
Since the beginning of 2009, a number of new plasma focus machines have been/are being commissioned including the INTI Plasma Focus in Malaysia, the NX3 in Singapore and the first plasma focus to be commissioned in a US university in recent times, the KSU Plasma Focus at Kansas State University which recorded its first fusion neutron emitting pinch on New Year's Eve 2009.
Electromagnetism
Electromagnetism is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction and gravitation...
acceleration and compression, a short-lived 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 is so hot and dense that it can cause 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...
and emit X-rays. The electromagnetic compression of the plasma is called a 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...
. It was invented in the early 1960s by J.W. Mather and also independently by N.V. Filippov. The plasma focus is similar to the high-intensity plasma gun device (HIPGD) (or just plasma gun), which ejects plasma in the form of a plasmoid
Plasmoid
A plasmoid is a coherent structure of plasma and magnetic fields. Plasmoids have been proposed to explain natural phenomena such as ball lightning, magnetic bubbles in the magnetosphere, and objects in cometary tails, in the solar wind, in the solar atmosphere, and in the heliospheric current sheet...
, without pinching it.
Applications
Intense bursts of X-rayX-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s and charged particles are emitted, as are 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...
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, when operated in 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 ...
. There is ongoing research that demonstrates potential applications as a soft X-ray source for next-generation microelectronics
Microelectronics
Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture of very small electronic components. Usually, but not always, this means micrometre-scale or smaller,. These devices are made from semiconductors...
lithography
Lithography
Lithography is a method for printing using a stone or a metal plate with a completely smooth surface...
, surface micromachining
Surface micromachining
Unlike Bulk micromachining, where a silicon substrate is selectively etched to produce structures, surface micromachining builds microstructures by deposition and etching of different structural layers on top of the substrate....
, pulsed X-ray and 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...
source for medical and security inspection applications and materials modification, among others.
For nuclear weapons applications, dense plasma focus devices can be used as an external 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...
. Other applications include simulation of nuclear explosions (for testing of the electronic equipment) and a short and intense neutron source useful for non-contact discovery or inspection of nuclear materials (uranium, plutonium).
Positive characteristics
An important characteristic of the dense plasma focus is that the energy densityEnergy density
Energy density is a term used for the amount of energy stored in a given system or region of space per unit volume. Often only the useful or extractable energy is quantified, which is to say that chemically inaccessible energy such as rest mass energy is ignored...
of the focused plasma is practically a constant over the whole range of machines, from sub-kilojoule machines to megajoule machines, when these machines are tuned for optimal operation. This means that a small table-top-sized plasma focus machine produces essentially the same plasma characteristics (temperature and density) as the largest plasma focus. Of course the larger machine will produce the larger volume of focused plasma with a corresponding longer lifetime and more radiation yield.
Even the smallest plasma focus has essentially the same dynamic characteristics as larger machines, producing the same plasma characteristics and the same radiation products. This is due to the scalability of plasma
Plasma scaling
The parameters of plasmas, including their spatial and temporal extent, vary by many orders of magnitude. Nevertheless, there are significant similarities in the behaviors of apparently disparate plasmas. Understanding the scaling of plasma behavior is of more than theoretical value...
phenomena.
See also plasmoid
Plasmoid
A plasmoid is a coherent structure of plasma and magnetic fields. Plasmoids have been proposed to explain natural phenomena such as ball lightning, magnetic bubbles in the magnetosphere, and objects in cometary tails, in the solar wind, in the solar atmosphere, and in the heliospheric current sheet...
, the self-contained magnetic plasma ball that may be produced by a dense plasma focus.
Operation
The charged bank of electrical capacitors (also called a Marx bank or Marx generatorMarx 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. Marx generators are often used to simulate the effects of lightning on power line gear and aviation equipment....
) is switched onto the anode. The gas breaks down. A rapidly rising electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
flows across the backwall electrical insulator, axisymmetrically, as depicted by the path (labeled 1) as shown in the fig. 1. The axisymmetric sheath of plasma current lifts off the insulator due to the interaction of the current with its own magnetic field (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:...
). The plasma sheath is accelerated axially, to position 2, and then to position 3, ending the axial phase of the device.
The whole process proceeds at many times the speed of sound
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....
in the ambient gas. As the current sheath continues to move axially, the portion in contact with the anode slides across the face of the anode, axisymmetrically. When the imploding front of the shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...
coalesces onto the axis, a reflected shock front emanates from the axis until it meets the driving current sheath which then forms the axisymmetric boundary of the pinched, or focused, hot plasma column.
The dense plasma column (akin to the Z-pinch
Z-pinch
In fusion power research, the Z-pinch, also known as zeta pinch or Bennett pinch , is a type of plasma confinement system that uses an electrical current in the plasma to generate a magnetic field that compresses it...
) rapidly 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...
es and undergoes instabilities and breaks up. The intense electromagnetic and particle bursts, collectively referred to as multi-radiation occur during the dense plasma and breakup phases. These critical phases last typically tens of nanoseconds for a small (kJ, 100 kA) focus to around a microsecond
Microsecond
A microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...
for a large (MJ, several MA) focus.
The whole process, including axial and radial phases, may last, for the Mather DPF, a few microseconds (for a small focus) to 10 microseconds (for a large focus). A Filippov focus has a very short axial phase compared to a Mather focus.
Design parameters
The fact that the plasma energy density is constant throughout the range of plasma focus devices, from big to small, is related to the value of a design parameter that needs to be kept at a certain value if the plasma focus is to operate efficiently. The critical 'speed' design parameter is, or the current linear density divided by the square root of the mass density of the fill gas.For example for neutron-optimised operation in deuterium the value of this critical parameter, experimentally observed over a range of machines from kilojoules to hundreds of kilojoules, is: 9 A/(m·Torr0.5), or 780 kA/(m·Pa0.5), with a remarkably small deviation of 10% over such a large range of sizes of machines.
Thus if we have a peak current of 180 kA we require an anode radius of 10 mm with a deuterium fill pressure of 4 Torr (533.3 Pa). The length of the anode has then to be matched to the risetime of the capacitor current in order to allow an average axial transit speed of the current sheath of just over 50 mm/μs. Thus a capacitor risetime of 3 μs requires a matched anode length of 160 mm.
The above example of peak current of 180 kA rising in 3 µs, anode radius and length of respectively 10 and 160 mm are close to the design parameters of the UNU/ICTP PFF (United Nations University/International Centre for Theoretical Physics Plasma Fusion Facility). This small table-top device was designed as a low-cost integrated experimental system for training and transfer to initiate/strengthen experimental plasma research in developing countries.
Current research
There is a network of ten identical DPF machines, operating in some eight countries and producing postgraduate students and research papers in machine optimization and diagnostics (soft x-rays, neutrons, electron and ion beams), applications (microlithography, micromachining, materials modification and fabrication, imaging and medical, astrophysical simulation) and modeling and computation. The network was organised by Sing Lee in 1986 and is coordinated by the Asian African Association for Plasma Training, AAAPT. A simulation package, the Lee Model, has been developed for this network but is applicable to all plasma focus devices. The code typically produces excellent agreement between computed and measured results, and is available for downloading as a Universal Plasma Focus Laboratory Facility. The Institute for Plasma Focus Studies IPFS was founded on 25 February 2008 to promote correct and innovative use of the Lee Model code and to encourage the application of plasma focus numerical experiments. IPFS research has already extended numerically-derived neutron scaling laws to multi-megajoule experiments. These await verification. Numerical experiments with the code have also resulted in the compilation of a global scaling law indicating that the well-known neutron saturation effect is better correlated to a scaling deterioration mechanism. This is due to the increasing dominance of the axial phase dynamic resistance as capacitor bank impedance decreases with increasing bank energy (capacitance).The International Centre for Dense Magnetised Plasmas (ICDMP) in Warsaw Poland, operates several plasma focus machines for an international research and training programme. Among these machines is one with energy capacity of 1 MJ making it one of the largest plasma focus devices in the world.
In Argentina there is an Inter-institutional Program for Plasma Focus Research since 1996, coordinated by a National Laboratory of Dense Magnetized Plasmas (www.pladema.net) in Tandil, Buenos Aires. The Program also cooperates with the Chilean Nuclear Energy Commission, and networks the Argentine National Energy Commission, the Scientific Council of Buenos Aires, the University of Center, the University of Mar del Plata, The University of Rosario, and the Institute of Plasma Physics of the University of Buenos Aires. The program operates six Plasma Focus Devices, developing applications, in particular ultrashort tomography and substance detection by neutron pulsed interrogation. Chile currently operates the facility SPEED-2, the largest Plasma Focus facility of the southern hemisphere. PLADEMA also contributed during the last decade with several mathematical models of Plasma Focus. The thermodynamic model was able to develop for the first time design maps combining geometrical and operational parameters, showing that there is always an optimum gun length and charging pressure which maximize the neutronic emissions. Currently there is a complete finite-elements code validated against numerous experiments, which can be used confidently as a design tool for Plasma Focus.
DPF for nuclear fusion power
Several groups have proposed that fusion powerFusion 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...
based on the DPF could be viable, possibly even with low-neutron fuel cycles
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...
like p-B11. The feasibility of net power from p-B11 in the DPF requires that the 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...
losses be reduced by quantum mechanical effects induced by the powerful magnetic field. The high magnetic field will also result in a high rate of emission of cyclotron radiation
Cyclotron radiation
Cyclotron radiation is electromagnetic radiation emitted by moving charged particles deflected by a magnetic field. The Lorentz force on the particles acts perpendicular to both the magnetic field lines and the particles' motion through them, creating an acceleration of charged particles that...
, but at the densities envisioned, where the plasma frequency is larger than the cyclotron frequency, most of this power will be reabsorbed before being lost from the plasma. Another advantage claimed is the capability of direct conversion of the energy of the fusion products into electricity, with an efficiency potentially above 70%. Experiments and computer simulations to investigate the capability of DPF for fusion power are underway at Lawrenceville Plasma Physics (LPP) under the direction of Eric Lerner
Eric Lerner
Eric J. Lerner is an American popular science writer, independent plasma researcher, and serves as the president of Lawrenceville Plasma Physics, Inc...
, who explained his "Focus Fusion" approach in a 2007 Google Tech Talk. On November 14, 2008, Lerner received funding for continued research, to test the scientific feasibility of Focus Fusion. On October 15, 2009, the DPF device "Focus Fusion-1" achieved its first pinch. On January 28th, 2011, LPP published initial results including experimental shots with considerably higher fusion yields than the historical DPF trend.
Since the beginning of 2009, a number of new plasma focus machines have been/are being commissioned including the INTI Plasma Focus in Malaysia, the NX3 in Singapore and the first plasma focus to be commissioned in a US university in recent times, the KSU Plasma Focus at Kansas State University which recorded its first fusion neutron emitting pinch on New Year's Eve 2009.
History
- 1958: Петров Д. П. и др., Мощный импульсный газовый разряд в камерах с проводящими стенками, в сб.: Физика плазмы и проблема управляемых термоядерных реакций, т. 4, Москва, 1958
- 1958: Hannes AlfvénHannes AlfvénHannes Olof Gösta Alfvén was a Swedish electrical engineer, plasma physicist and winner of the 1970 Nobel Prize in Physics for his work on magnetohydrodynamics . He described the class of MHD waves now known as Alfvén waves...
: Proceedings of the Second International Conference on Peaceful Uses of Atomic Energy (United Nations), 31, 3 - 1960: H Alfven, L Lindberg and P Mitlid, "Experiments with plasma rings" (1961) Journal of Nuclear Energy. Part C, Plasma Physics, Accelerators, Thermonuclear Research, Volume 1, Issue 3, pp. 116–120
- 1960: Lindberg, L., E. Witalis and C. T. Jacobsen, "Experiments with plasma rings" (1960) Nature 185:452.
- 1961: Hannes Alfvén: Plasma Ring Experiment in "On the Origin of Cosmic Magnetic Fields" (1961) Astrophysical Journal, vol. 133, p. 1049
- 1961: Lindberg, L. & Jacobsen, C., "On the Amplification of the Poloidal Magnetic Flux in a Plasma" (1961) Astrophysical Journal, vol. 133, p. 1043
- 1962: Filippov. N.V., et al., "Dense, High-Temperature Plasma in a Noncylindrical 2-pinch Compression" (1962) 'Nuclear Fusion Supplement'. Pt. 2, 577
- 1969: Buckwald, Robert Allen, "Dense Plasma Focus Formation by Disk Symmetry" (1969) ThesisThesisA dissertation or thesis is a document submitted in support of candidature for an academic degree or professional qualification presenting the author's research and findings...
, Ohio State UniversityOhio State UniversityThe Ohio State University, commonly referred to as Ohio State, is a public research university located in Columbus, Ohio. It was originally founded in 1870 as a land-grant university and is currently the third largest university campus in the United States...
.
External links
- Plasma Radiation Source Lab at the National Institute of Education in Singapore
- Plasma Focus Laboratory, International Centre for Dense Magnetised Plasmas, Warsaw, Poland
- Optics and Plasma Physics Group,Pontificia Universidad Católica de Chile
- Paper by Leopoldo Soto (Chilean Nuclear Energy Commission, Thermonucluar Plasma Department): New trends and future perspectives on plasma focus research
- Focus Fusion Society
- Abdus Salam ICTP Plasma Focus Laboratory. http://mlab.ictp.it/plasma/pfd.html
- Numerical Simulation Package: Universal Plasma Focus Laboratory Facility at INTI-UC. http://www.intimal.edu.my/school/fas/UFLF/
- Dense Plasma Focus Network in Argentina.
- Institute for Plasma Focus Studies (IPFS).
- Research papers published in 2008 by IPFS staff. http://www.plasmafocus.net/Papers/listofpapers.htm
- Fusion Energy Site with links.