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{{Short description|Proposed aircraft stealth technology}}
'''Plasma stealth''' is a proposed process to use ionized gas ([[plasma (physics)|plasma]]) to reduce the [[radar cross-section]] (RCS) of an [[aircraft]]. Interactions between [[electromagnetic radiation]] and ionized gas have been extensively studied for many purposes, including concealing aircraft from radar as [[stealth technology]]. Various methods might plausibly be able to form a layer or cloud of plasma around a [[vehicle]] to deflect or absorb radar, from simpler electrostatic or [[radio frequency]] (RF) discharges to more complex laser discharges.<ref name="laserplasma">{{cite conference▼
| author=I.V. Adamovich▼
▲'''Plasma stealth''' is a proposed process to use ionized gas ([[plasma (physics)|plasma]]) to reduce the [[radar cross-section]] (RCS) of an [[aircraft]]. Interactions between [[electromagnetic radiation]] and ionized gas have been extensively studied for many purposes, including concealing aircraft from radar as [[stealth technology]]. Various methods might plausibly be able to form a layer or cloud of plasma around a [[vehicle]] to deflect or absorb radar, from simpler electrostatic or [[radio frequency]]
| author2=J. W. Rich▼
| author3=A.P. Chernukho▼
| author4=S.A. Zhdanok▼
| title=Analysis of the Power Budget and Stability of High-Pressure Nonequilibrium Air Plasmas▼
| booktitle=Proceedings of 31st AIAA Plasmadynamics and Lasers Conference, June 19–22,2000▼
| date=2000▼
▲ |book-title
| pages=Paper 00–2418▼
| url=http://rclsgi.eng.ohio-state.edu/~adamovic/netl/PowerBudgtHighPlasma.pdf▼
}}</ref> It is theoretically possible to reduce RCS in this way, but it may be very difficult to do so in practice.▼
|url-status = dead
|archive-url = https://web.archive.org/web/20060910192951/http://rclsgi.eng.ohio-state.edu/~adamovic/netl/PowerBudgtHighPlasma.pdf
|archive-date = 2006-09-10
▲}}</ref> It is theoretically possible to reduce RCS in this way, but it may be very difficult to do so in practice. Some Russian missiles e.g. the [[3M22 Zircon]] (SS-N-33) and [[Kh-47M2 Kinzhal]] missiles have been reported to make use of plasma stealth.
==First claims==
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}}</ref>
During Project OXCART, the operation of the [[Lockheed A-12]] reconnaissance aircraft, the CIA funded an attempt to reduce the RCS of the A-12's [[inlet cone]]s. Known as Project KEMPSTER, this used an electron beam generator to create a cloud of ionization in front of each inlet. The system was flight tested but was never deployed on operational A-12s or [[SR-71 Blackbird|SR-71s]].<ref>[http://www.blackbirds.net/sr71/oxcart/successortou2.html ''The U-2's Intended Successor: Project Oxcart 1956-1968'', approved for release by the CIA in October 1994. Retrieved: 26 January 2007].</ref> The A-12 also had the capability to use a [[cesium]]-based fuel additive called "A-50" to ionize the exhaust gases, thus blocking radar waves from reflecting off the aft quadrant and engine exhaust pipes. Cesium was used because it was easily ionized by the hot exhaust gases. Radar physicist Ed Lovick Jr. claimed this additive saved the A-12 program.<ref>{{cite web|url=https://www.thedrive.com/the-war-zone/29787/the-sr-71-blackbirds-predecessor-created-plasma-stealth-by-burning-cesium-laced-fuel|author=Joseph Trevithick and Tyler Rogoway|date=September 12, 2019|title=The SR-71 Blackbird's Predecessor Created "Plasma Stealth" By Burning Cesium-Laced Fuel|publisher=The Drive}}</ref>
In 1992, Hughes Research Laboratory conducted a research project to study electromagnetic wave propagation in unmagnetized plasma. A series of high voltage spark gaps were used to generate UV radiation, which creates plasma via photoionization in a waveguide. Plasma filled missile
Despite the apparent technical difficulty of designing a plasma stealth device for combat aircraft, there are claims that a system was offered for export by [[Russia]] in 1999. In January 1999, the Russian [[ITAR-TASS]] news agency published an interview with Doctor [[Anatoliy Koroteyev]], the director of the Keldysh Research Center (FKA Scientific Research Institute for Thermal Processes), who talked about the plasma stealth device developed by his organization. The claim was particularly interesting in light of the solid scientific reputation of Dr. Koroteyev and the Institute for Thermal Processes,{{Citation needed|date=April 2010}} which is one of the top scientific research organizations in the world in the field of fundamental physics.<ref>Nikolay Novichkov.''Russian scientists created revolutionary technologies for reducing radar visibility of aircraft''. "ITAR-TASS", January 20, 1999.</ref>
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{{Main|Plasma (physics)}}
A plasma is a ''[[Plasma (physics)#
Plasmas can interact strongly with electromagnetic radiation: this is why plasmas might plausibly be used to modify an object's radar signature. Interaction between plasma and electromagnetic radiation is strongly dependent on the physical properties and parameters of the plasma, most notably the electron temperature and plasma density.
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:<math>\omega_{pe} = (4\pi n_ee^2/m_e)^{1/2} = 5.64 \times 10^4 n_e^{1/2} \mbox{rad/s} = 9000 \times n_e^{1/2} \mbox{Hz} </math>
Plasmas can have a wide range of values in both temperature and density; plasma temperatures range from close to absolute zero and to well beyond 10<sup>9</sup> [[kelvin]]s (for comparison, tungsten melts at 3700 kelvins), and plasma may contain less than one particle per cubic metre
Plasmas support a wide range of waves, but for unmagnetised plasmas, the most relevant are the [[Langmuir wave]]s, corresponding to a dynamic compression of the electrons. For magnetised plasmas, many different wave modes can be excited which might interact with radiation at radar frequencies.
== Absorption of EM radiation ==
When [[Electromagnetic radiation|electromagnetic]] waves, such as radar signals, propagate into a conductive plasma, ions and electrons are displaced as a result of the time varying electric and magnetic fields. The wave field gives energy to the particles. The particles generally return some fraction of the energy they have gained to the wave, but some energy may be permanently absorbed as heat by processes like scattering or resonant acceleration, or transferred into other wave types by [[mode conversion]] or nonlinear effects. A plasma can, at least in principle, absorb all the energy in an incoming wave, and this is the key to plasma stealth. However, plasma stealth implies a substantial reduction of an aircraft's [[Radar cross-section|RCS]], making it more difficult (but not necessarily impossible) to detect. The mere fact of detection of an aircraft by a radar does not guarantee an accurate targeting solution needed to intercept the aircraft or to engage it with missiles. A reduction in RCS also results in a proportional reduction in detection range, allowing an aircraft to get closer to the radar before being detected.
The central issue here is frequency of the incoming signal. A plasma will simply reflect radio waves below a certain frequency (characteristic electron plasma frequency). This is the basic principle of short wave radios and long-range communications, because low-frequency radio signals bounce between the Earth and the ionosphere and may therefore travel long distances. Early-warning over-the-horizon radars utilize such low-frequency radio waves (typically lower than 50 MHz). Most military airborne and air defense radars, however, operate in VHF, UHF, and microwave band, which have frequencies higher than the characteristic plasma frequency of ionosphere, therefore microwave can penetrate the ionosphere and communication between the ground and communication satellites demonstrates is possible. (''Some'' frequencies can penetrate the ionosphere).
Plasma surrounding an aircraft might be able to absorb incoming radiation, and therefore reduces signal reflection from the metal parts of the aircraft: the aircraft would then be effectively invisible to radar at long range due to weak signals received.<ref name=Chung1>{{cite book|author1=Shen Shou Max Chung|editor1-last=Wang|editor1-first=Wen-Qin|title=Radar Systems: Technology, Principles and Applications|date=2013|publisher=NOVA Publishers|location=Hauppauge, NY|isbn=978-1-62417-884-9|pages=1–44|edition=1|chapter-url=https://www.novapublishers.com/catalog/product_info.php?products_id=42399|chapter=Chapter 1: Manipulation of Radar Cross Sections with Plasma|doi=10.13140/2.1.4674.4327}}</ref> A plasma might also be used to modify the reflected waves to confuse the opponent's radar system: for example, frequency-shifting the reflected radiation would frustrate Doppler filtering and might make the reflected radiation more difficult to distinguish from noise.
Control of plasma properties like density and temperature is important for a functioning plasma stealth device, and it may be necessary to dynamically adjust the plasma density, temperature, or combinations, or the magnetic field, in order to effectively defeat different types of radar systems. The great advantage Plasma Stealth possesses over traditional
Plasma stealth technology also faces various technical problems. For example, the plasma itself emits EM radiation,
▲|bibcode = 2009ITPS...37.2116C }}</ref> Chung studied the radar cross change of a metal cone when it is covered with plasma, a phenomenon that occurs during reentry into the atmosphere.<ref name=Chung2>{{cite journal|last1=Chung|first1=Shen Shou Max|title=FDTD Simulations on Radar Cross Sections of Metal Cone and Plasma Covered Metal Cone|journal=Vacuum|date=Feb 8, 2012|volume=86|issue=7|pages=970–984|doi=10.1016/j.vacuum.2011.08.016|url=http://www.sciencedirect.com/science/article/pii/S0042207X11003411|publisher=ELSEVIER|bibcode = 2012Vacuu..86..970M }}</ref> Chung simulated the radar cross section of a generic satellite, and also the radar cross section when it is covered with artificially generated plasma cones.<ref name=Chung3>{{cite journal|last1=Chung|first1=Shen Shou Max|title=Simulation on Change of Generic Satellite Radar Cross Section via Artificially Created Plasma Sprays|journal=Plasma Source Science and Technology|date=Mar 30, 2016|volume=25|pages=035004|doi=10.1088/0963-0252/25/3/035004|bibcode = 2016PSST...25c5004C }}</ref>
== Theoretical work with Sputnik ==
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==See also==
* [[Stealth technology]]
* [[
* [[Multi-spectral camouflage]]
* [[Cloaking device]]
* [[Penetration aid]]
==References==
{{Reflist|30em}}
[[Category:Radar]]
[[Category:Plasma
[[Category:Stealth technology]]
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