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Encyclopedia > Dense plasma focus


A Dense Plasma Focus (DPF) is a plasma machine that produces, by electromagnetic acceleration and compression, short-lived plasma that is so hot and dense that it becomes a copious multi-radiation source. It was invented in the early 1960s by J.W. Mather and also independently by N.V. Filippov. It is also called a high-intensity plasma gun device (HIPGD), or just plasma gun. The word plasma has a Greek root which means to be formed or molded (the word plastic shares this root). ... Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. ... The 1960s decade refers to the years from 1960 to 1969, inclusive. ...

Contents


Applications

Intense bursts of x-rays and charged particles are emitted as are nuclear fusion neutrons 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. In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance of one atom in 6500 of hydrogen. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... Microelectronics - Wikipedia, the free encyclopedia /**/ @import /skins-1. ... Surface micromachining is a process used to produce micromachinery or MEMS. Unlike Bulk micromachining, where a silicon substrate (wafer) is selectively etched to produces structures, surface micromachining is based on the deposition and etching of different structural layers. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ...


Positive characteristics

An important characteristic of the dense plasma focus is that the energy density 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 life-time and more radiation yield. Energy density is the amount of potential energy stored in a given system or region of space per unit volume. ...


But it is remarkable that even the smallest plasma focus has essentially the same dynamic characteristics as larger machines, producing the same plasma characteristics and the same radiation products and radiation characteristics.


See also plasmoid, the self-contained magnetic plasma ball that may be produced by a dense plasma focus. A plasmoid is a coherent structure of plasma and magnetic fields. ...


How it works

The basic configuration of the Mather type
The basic configuration of the Mather type
Typical design, focusing signatures (on voltage and current waveforms, 3 microsec from start to voltage spike) and the radial implosion and breakup dynamics shown in a 6-frame nitrogen laser shadowgraphic sequence over a period of about 40 ns.
Typical design, focusing signatures (on voltage and current waveforms, 3 microsec from start to voltage spike) and the radial implosion and breakup dynamics shown in a 6-frame nitrogen laser shadowgraphic sequence over a period of about 40 ns.

The charged bank of electrical capacitors 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 (J×B force). The plasma sheath is accelerated axially, to position 2, and then to position 3, ending the axial phase of the device. Image File history File links DPFfig1_. ... Image File history File links DPFfig1_. ... ImageMetadata File history File links DPFfig2_. ... ImageMetadata File history File links DPFfig2_. ... Various types of capacitors A capacitor is a device that stores energy in the electric field created between a pair of conductors on which equal but opposite electric charges have been placed. ... In electricity, current is the rate of flow of charges, usually through a metal wire or some other electrical conductor. ... // Definition An Insulator is a material or object which resists the flow of heat (thermal insulators) or electric charge (electrical insulators). ...


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 speed of sound c (from Latin celeritas, velocity) varies depending on the medium through which the sound waves pass. ... In fluid dynamics, a shock wave is a nonlinear or discontinuous pressure wave. ...


The dense plasma column (akin to the Z-pinch) rapidly 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 Z machine at Sandia National Laboratories in Albuquerque, New Mexico. ... A nanosecond is an SI derived unit of time equal to 10-9 of a second. ... A microsecond is an SI unit of time equal to one millionth (10-6) of a second. ...


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 {{I over a} over sqrt{p}}, 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: 90 (kA/cm)/(Torr)1/2 (780 kA/(m·Pa1/2)) 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 1 cm with a deuterium fill pressure of 4 torrs. 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 5cm/microsec. Thus a capacitor risetime of 3 microsecond requires a matched anode length of 16 cm.


The above example of peak current of 180 kA rising in 3 µs, anode radius and length of respectively 1 and 16 cm are close to the design parameters of the UNU/ICTP PFF (United Nations University/International Centre for Theoretical Physics Plasma Fusion Facility)[1]. 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 [2].


Current research

There is now a network (coordinated by the Asian African Association for Plasma Training, AAAPT) of 10 such identical DPF machines, operating in some 8 countries 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 AAAPT, or Asian African Association for Plasma Training is an organization/network formed on 7 June 1988 by nineteen institutions from 12 countries as an answer to the needs of small research groups in developing countries wanting but not having facilities to carry out plasma research. ...


This DPF network was organised by S. Lee from 1986, taking advantage of the fact that even a small DPF can be used to study all the plasma phenomena that a big DPF has access to. 1986 (MCMLXXXVI) is a common year starting on Wednesday of the Gregorian calendar. ...


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 device in the world.


DPF for Nuclear Fusion Power

Several groups have claimed the DPF could prove extremely viable for Nuclear fusion Power, claiming a DPF can produce temperatures high enough for p+B11 fusion, and that the powerful magnetic field can reduce electron ion collision and thus reduce Bremsstrahlung loss. Also a DPF would be well capable of connecting to a direct conversion decelerator that would decelerate the particle stream produced by the DPF and convert its motion into electricity through magnetic flux, efficiencies above 70% for direct conversion are claimed, and that the device would be cheaper then a steam turbine generator. So far only minor experiment and computer simulations have been done to verify the capability of DPF for fusion power. The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... The Sun is a natural fusion reactor. ... Bremsstrahlung   listen?, German for braking radiation, is electromagnetic radiation produced by the acceleration of a charged particle, such as an electron, when deflected by another charged particle, such as an atomic nucleus. ...


History

  • 1958: Hannes Alfvén: 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) Thesis, Ohio State University.

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
  • Focus Fusion Society

  Results from FactBites:
 
Plasma (physics) - Wikipedia, the free encyclopedia (2819 words)
In physics and chemistry, a plasma is an ionized gas, and is usually considered to be a distinct phase of matter.
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For many purposes the electric field in a plasma may be treated as zero, although when current flows the voltage drop, though small, is finite, and density gradients are usually associated with an electric field according to the Boltzmann relation.
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