Editing Magnetohydrodynamic drive

{{Short description|Vehicle propulsion using electromagnetic fields}}
{{Original research|date=April 2020|discuss=Talk:Magnetohydrodynamic Drive#Fact or fiction}}
[[File:Yamato1 1.jpg|thumb|''[[Yamato 1]]'' on display in [[Kobe]], Japan. The first working full-scale MHD ship.]]
A '''magnetohydrodynamic drive''' or '''MHD accelerator''' is a method for propelling vehicles using only [[Electric field|electric]] and [[magnetic field]]s with no [[moving parts]], accelerating an [[Electrical resistivity and conductivity|electrically conductive]] [[propellant]] ([[liquid]] or [[gas]]) with [[magnetohydrodynamics]]. The [[fluid]] is directed to the rear and as a [[Reaction (physics)|reaction]], the vehicle accelerates forward.<ref name="PopMech 1990">{{cite magazine
 |last=Dane |first=Abe
 |title=100 mph Jet Ships
 |date=August 1990
 |magazine=Popular Mechanics
 |pages=60–62
 |url=http://ayuba.fr/pdf/popmech_aug1990.pdf
 |access-date=2018-04-04
}}</ref><ref name="PopSci 1992">{{cite magazine
 |last=Normile |first=Dennis
 |title=Superconductivity goes to sea
 |date=November 1992
 |magazine=Popular Science
 |publisher=Bonnier Corporation
 |pages=80–85
 |url=http://ayuba.fr/pdf/popsci_nov1992.pdf
 |access-date=2018-04-04
}}</ref>

Studies examining MHD in the field of [[marine propulsion]] began in the late 1950s.<ref name="Way 1958">{{cite report
 |last1=Way |first1=S.
 |title=Examination of Bipolar Electric and Magnetic Fields for Submarine Propulsion
 |date=15 October 1958
 |publisher=US Navy Bureau of Ships
 |id=Preliminary Memorandum Communication 
}}</ref><ref name="Rice 1961">{{cite patent
|country=US
|number=2997013
|status= patent
|title= Propulsion System
|gdate=1961-08-22
|fdate=1958-07-18
|pridate=1958-07-18
|inventor=Warren A. Rice
|invent1=Rice, Warren A.
|assign1=Carl E. Grebe 
}}</ref><ref name="Friauf 1961">{{cite journal
 |last1=Friauf |first1=J.B.
 |title=Electromagnetic ship propulsion
 |date=February 1961
 |journal=Journal of the American Society for Naval Engineers
 |volume=73
 |issue=1
 |pages=139–142
 |doi=10.1111/j.1559-3584.1961.tb02428.x
 |url=http://ayuba.fr/pdf/friauf1961.pdf
 |access-date=2018-04-04
}}
</ref><ref name="Phillips 1962">{{cite journal
 |last1=Phillips |first1=O.M.
 |title=The prospects for magnetohydrodynamic ship propulsion
 |date=1962
 |journal=Journal of Ship Research
 |volume=43
 |pages=43–51
 }}</ref><ref name="Doragh 1963">{{cite journal
 |last1=Doragh |first1=R.A.
 |title=Magnetohydrodynamic Ship Propulsion using Superconducting Magnets
 |date=November 1963
 |journal=Transactions of the Society of Naval Architects and Marine Engineers
 |volume=71
 |pages=370–386
}}</ref>

Few large-scale marine prototypes have been built, limited by the low [[electrical conductivity]] of [[seawater]]. Increasing [[current density]] is limited by [[Joule heating]] and water [[electrolysis]] in the vicinity of [[electrode]]s, and increasing the magnetic field strength is limited by the cost, size and weight (as well as technological limitations) of [[electromagnet]]s and the power available to feed them.<ref name="PLOS">{{cite journal
 |last1=Cébron |first1=David
 |last2=Viroulet |first2=Sylvain
 |last3=Vidal |first3=Jérémie
 |last4=Masson |first4=Jean-Paul
 |last5=Viroulet |first5=Philippe
 |title=Experimental and Theoretical Study of Magnetohydrodynamic Ship Models
 |year=2017
 |journal=PLOS ONE
 |volume=12
 |issue=6
 |pages=e0178599
 |doi=10.1371/journal.pone.0178599
 |pmid=28665941
 |pmc=5493298
 |arxiv=1707.02743|bibcode=2017PLoSO..1278599C|doi-access=free
 }}</ref><ref name="TPT">{{cite journal 
 |last1=Overduin |first1=James
 |last2=Polyak |first2= Viktor
 |last3=Rutah |first3=Anjalee
 |last4= Sebastian |first4= Thomas
 |last5=Selway |first5=Jim
 |last6=Zile |first6=Daniel
 |title=The Hunt for Red October II: A magnetohydrodynamic boat demonstration for introductory physics
 |date=November 2017
 |journal=The Physics Teacher
 |volume=55
 |issue=8
 |pages=460–466
 |doi=10.1119/1.5008337
 |url=https://www.researchgate.net/publication/320439957
|bibcode=2017PhTea..55..460O}}</ref> In 2023 [[DARPA]] launched the PUMP program to build a marine engine using superconducting magnets expected to reach a field strength of 20 [[Tesla (unit)|Tesla]].<ref>{{Cite web |last=Wang |first=Brian |date=2023-05-25 |title=DARPA Works to Make A Practical Ultraquiet Superconducting Magnet Drive for Submarines {{!}} NextBigFuture.com |url=https://www.nextbigfuture.com/2023/05/darpa-works-to-make-a-practical-ultraquiet-superconducting-magnet-drive-for-submarines.html |access-date=2023-05-25 |language=en-US}}</ref>

Stronger technical limitations apply to air-breathing MHD propulsion (where ambient [[Atmosphere of Earth|air]] is ionized) that is still limited to theoretical concepts and early experiments.<ref name="Popular Mechanics 1995">{{cite magazine
 |last1=Pope |first1=Gregory T.
 |title=Fly by microwaves
 |date=September 1995
 |magazine=Popular Mechanics
 |pages=44–45
 |url=http://ayuba.fr/pdf/popmech1995.pdf
 }}</ref><ref name="Weier-Shatrov-Gerbeth 2007">{{cite book |editor1-last=Molokov |editor1-first=Sergei S. |editor2-last=Moreau |editor2-first=R. |editor3-last= Moffatt |editor3-first=H. Keith |title=Magnetohydrodynamics: Historical Evolution and Trends |last1=Weier |first1=Tom |last2=Shatrov |first2=Victor |last3=Gerbeth |first3=Gunter |chapter=Flow Control and Propulsion in Poor Conductors |pages=295–312|publisher=Springer Science+Business Media |date=2007 |isbn=978-1-4020-4832-6 |doi=10.1007/978-1-4020-4833-3}}</ref><ref name="NAB">{{cite web
 |author=<!--Not stated-->
 |title=What is the Russian Ayaks aircraft?
 |date=30 March 2015
 |website=North Atlantic Blog
 |url=https://northatlanticblog.wordpress.com/2015/03/30/what-is-the-russian-ayaks-aircraft/
}}</ref>

[[Plasma propulsion engine]]s using magnetohydrodynamics for [[space exploration]] have also been actively studied as such [[Electrically powered spacecraft propulsion#Electromagnetic|electromagnetic propulsion]] offers high [[thrust]] and high [[specific impulse]] at the same time, and the propellant would last much longer than in [[Rocket engine|chemical rockets]].<ref name="Choueiri 2009">{{cite magazine
 |last1=Choueiri
 |first1=Edgar Y.
 |title=New dawn of electric rocket
 |date=February 2009
 |magazine=Scientific American
 |volume=30
 |issue=2
 |pages=58–65
 |url=http://alfven.princeton.edu/publications/choueiri-sciam-2009
 |format=PDF
 |doi=10.1038/scientificamerican0209-58
 |bibcode=2009SciAm.300b..58C
 |access-date=2018-04-04
 |archive-date=2016-10-18
 |archive-url=https://web.archive.org/web/20161018201525/http://alfven.princeton.edu/publications/choueiri-sciam-2009
 |url-status=dead
 }}</ref>

== Principle ==
{{Main|Lorentz force}}
{{see also|Magnetohydrodynamic converter}}
[[File:Right hand rule cross product F=J×B.svg|thumb|Illustration of the right-hand rule for the Lorentz force, cross product of an electric current with a magnetic field.]]

The working principle involves the acceleration of an electrically conductive [[fluid]] (which can be a [[liquid]] or an [[Ionization|ionized]] [[gas]] called a [[Plasma (physics)|plasma]]) by the [[Lorentz force]], resulting from the [[cross product]] of an [[electric current]] (motion of [[charge carrier]]s accelerated by an [[electric field]] applied between two [[electrode]]s) with a [[perpendicular]] [[magnetic field]]. The Lorentz force accelerates all [[charged particles]], positive and negative species (in opposite directions). If either positive or negative species dominate the vehicle is put in motion in the opposite direction from the net charge.

This is the same working principle as an [[electric motor]] (more exactly a [[linear motor]]) except that in an MHD drive, the solid moving [[Rotor (electric)|rotor]] is replaced by the fluid acting directly as the [[propellant]]. As with all [[Electromagnetism|electromagnetic]] devices, an MHD accelerator is reversible: if the ambient [[working fluid]] is moving relatively to the magnetic field, [[Electric dipole moment|charge separation]] induces an [[voltage|electric potential difference]] that can be harnessed with [[electrode]]s: the device then acts as a [[Electric generator|power source]] with no moving parts, transforming the [[kinetic energy]] of the incoming fluid into [[electricity]], called an [[Magnetohydrodynamic generator|MHD generator]].

[[File:MHD converters (generator and accelerator).svg|thumb|512px|Crossed-field magnetohydrodynamic converters (linear Faraday type with segmented electrodes). A: MHD generator mode. B: MHD accelerator mode.|center]]

As the Lorentz force in an MHD converter does not act on a single isolated charged particle nor on electrons in a solid [[Electrical wiring|electrical wire]], but on a continuous [[Charge density|charge distribution]] in motion, it is a "volumetric" (body) force, a force per unit volume:

:<math>\mathbf{f} = \rho \mathbf{E} + \mathbf{J} \times \mathbf{B}\,\!</math>

where '''f''' is the ''force density'' (force per unit volume), ''ρ'' the [[charge density]] (charge per unit volume), '''E''' the [[electric field]], '''J''' the [[current density]] (current per unit area) and '''B''' the [[magnetic field]].{{clarify|date=July 2020}}

==Typology==

MHD thrusters are classified in two categories according to the way the electromagnetic fields operate:
* '''Conduction devices''' when a [[direct current]] flows in the fluid due to an applied voltage between pairs of electrodes, the magnetic field being steady.
* '''Induction devices''' when [[alternating current]]s are [[Electromagnetic induction|induced]] by a rapidly varying magnetic field, as [[eddy current]]s. No electrodes are required in this case.

As induction MHD accelerators are electrodeless, they do not exhibit the common issues related to conduction systems (especially Joule heating, bubbles and [[redox]] from electrolysis) but need much more intense peak magnetic fields to operate. Since one of the biggest issues with such thrusters is the limited energy available on-board, induction MHD drives have not been developed out of the laboratory.

Both systems can put the working fluid in motion according to two main designs:
* '''Internal flow''' when the fluid is accelerated within and propelled back out of a [[propelling nozzle|nozzle]] of tubular or ring-shaped [[Cross section (geometry)|cross-section]], the MHD interaction being concentrated within the pipe (similarly to [[Rocket engine|rocket]] or [[jet engine]]s).
* '''External flow''' when the fluid is accelerated around the whole [[wetted area]] of the vehicle, the electromagnetic fields extending around the body of the vehicle. The propulsion force results from the pressure distribution on the shell (as [[Lift (force)|lift]] on a [[wing]], or how [[ciliate]] [[microorganism]]s such as ''[[Paramecium]]'' move water around them).

Internal flow systems concentrate the MHD interaction in a limited volume, preserving [[Stealth technology#Acoustics|stealth]] characteristics. External field systems on the contrary have the ability to act on a very large expanse of surrounding water volume with higher efficiency and the ability to decrease [[Drag (physics)|drag]], increasing the efficiency even further.<ref name="Way 1968">{{cite journal |last1=Way |first1=S. |date=1968 |title=Electromagnetic propulsion for cargo submarines |url=http://ayuba.fr/pdf/way1968.pdf |journal=Journal of Hydronautics |volume=2 |issue=2 |pages=49–57 |doi=10.2514/3.62773 |access-date=2018-04-04}}</ref>

===Marine propulsion===
[[File:Magnetohydrodynamic drive tube.jpg|thumb|A view through a tube in the thruster of ''Yamato I,'' at the Ship Science Museum in Tokyo. The electrode plates are visible top and bottom.]]
[[File:Magnetohydrodynamic drive.jpg|thumb|A view of the end of the thruster unit from ''Yamato I,'' at the Ship Science Museum in Tokyo]]
MHD has no moving parts, which means that a good design might be silent, reliable, and efficient. Additionally, the MHD design eliminates many of the wear and friction pieces of the [[Powertrain|drivetrain]] with a directly driven [[propeller]] by an engine. Problems with current technologies include expense and slow speed compared to a propeller driven by an engine.<ref name="PLOS" /><ref name="TPT" /> The extra expense is from the large generator that must be driven by an engine. Such a large generator is not required when an engine directly drives a propeller.

The first prototype, a 3-meter (10-feet) long submarine called EMS-1, was designed and tested in 1966 by Stewart Way, a professor of mechanical engineering at the [[University of California, Santa Barbara]]. Way, on leave from his job at [[Westinghouse Electric (1886)|Westinghouse Electric]], assigned his senior year undergraduate students to build the operational unit. This MHD submarine operated on batteries delivering power to electrodes and electromagnets, which produced a magnetic field of 0.015 tesla. The cruise speed was about 0.4 meter per second (15 inches per second) during the test in the bay of [[Santa Barbara, California]], in accordance with theoretical predictions.<ref>{{cite magazine |title=Run Silent, Run Electromagnetic |date=1966-09-23 |magazine=[[Time (magazine)|Time]] |url=http://www.time.com/time/magazine/article/0,9171,842848-1,00.html|archive-url=https://web.archive.org/web/20090114084102/http://www.time.com/time/magazine/article/0,9171,842848-1,00.html|url-status=dead|archive-date=January 14, 2009}}</ref><ref name="EMS-1 video">{{YouTube|id= RNMxlEfwdEc|title="EMS-1 electromagnetic submarine on US television (1966)"}}</ref><ref name="Way 1967b">{{cite conference |last1=Way |first1=S. |last2=Devlin |first2=C. |date=July 1967 |title=Prospects for the Electromagnetic Submarine |conference=AIAA 3rd Propulsion Joint Specialist Conference |location=Washington, D.C. |book-title=Paper 67-432}}</ref><ref name="Way 1968" />

Later, a Japanese prototype, the 3.6-meter long "ST-500", achieved speeds of up to 0.6&nbsp;m/s in 1979.<ref name="ICEC">A. Iwata, Y. Saji and S. Sato, "Construction of Model Ship ST-500 with Superconducting Electromagnetic Thrust System", in Proceedings of the 8th International Cryogenic Engineering Conference (ICEC 8), edited by C. Rizzuto (IPC Science and Technology, 1980), pp. 775–784.</ref>

In 1991, the world's first full-size prototype ''[[Yamato 1]]'' was completed in [[Japan]] after six years of [[research and development]] (R&D) by the [[Ship & Ocean Foundation]] (later known as the [[Ocean Policy Research Foundation]]). The ship successfully carried a crew of ten plus passengers at speeds of up to {{convert|15|km/h|knot|abbr=on}} in [[Kobe]] Harbour in June 1992.<ref name="PopSci 1992" /><ref name="BMESJ">{{cite journal
 |last1=Takezawa
 |first1=Setsuo
 |last2=Tamama
 |first2=Hiroshi
 |last3=Sugawawa
 |first3=Kazumi
 |last4=Sakai
 |first4=Hiroshi
 |last5=Matsuyama
 |first5=Chiaki
 |last6=Morita
 |first6=Hiroaki
 |last7=Suzuki
 |first7=Hiromi
 |last8=Ueyama
 |first8=Yoshihiro
 |title=Operation of the thruster for superconducting electromagnetohydrodynamic propulsion ship YAMATO-1
 |date=March 1995
 |journal=Bulletin of Marine Engineering Society of Japan
 |volume=23
 |issue=1
 |pages=46–55
 |url=http://www.jime.jp/e/publication/bulletin/english/pdf/mv23n011995p46.pdf
 |url-status=dead
 |archive-url=https://web.archive.org/web/20171215134832/http://www.jime.jp/e/publication/bulletin/english/pdf/mv23n011995p46.pdf
 |archive-date=2017-12-15
 |access-date=2018-04-04
 }}</ref>

Small-scale ship models were later built and studied extensively in the laboratory, leading to successful comparisons between the measurements and the theoretical prediction of ship terminal speeds.<ref name="PLOS" /><ref name="TPT" />

Military research about underwater MHD propulsion included high-speed [[torpedo]]es, [[remotely operated underwater vehicle]]s (ROV), [[autonomous underwater vehicle]]s (AUV), up to larger ones such as [[submarine]]s.<ref name="Lin 1990">{{cite report
 |last1=Lin |first1=T. F.
 |last2=Gilbert |first2=J. B
 |last3=Kossowsky |first3=R.
 |title=Sea-water magnetohydrodynamic propulsion for next-generation undersea vehicles
 |date=February 1990
 |publisher=Applied Research Laboratory, Pennsylvania State University
 |s2cid=35847351
 |id=US Navy/ONR Annual Report AD-A218 318
 |url=https://pdfs.semanticscholar.org/5e62/d4db0b04b871207f2dfab7102a19ad649c75.pdf |archive-url=https://web.archive.org/web/20180405152902/https://pdfs.semanticscholar.org/5e62/d4db0b04b871207f2dfab7102a19ad649c75.pdf |url-status=dead |archive-date=2018-04-05 |access-date=2018-04-04
}}</ref>

===Aircraft propulsion===
{{see also|Flow control (fluid)}}

====Passive flow control====
First studies of the interaction of plasmas with [[Hypersonic speed|hypersonic flows]] around vehicles date back to the late 1950s, with the concept of a new kind of [[Atmospheric entry#Thermal protection systems|thermal protection system]] for [[space capsule]]s during high-speed [[Atmospheric entry|reentry]]. As low-pressure air is naturally ionized at such very high velocities and altitude, it was thought to use the effect of a magnetic field produced by an electromagnet to replace [[Atmospheric entry#Ablative|thermal ablative shields]] by a "magnetic shield". Hypersonic ionized flow interacts with the magnetic field, inducing eddy currents in the plasma. The current combines with the magnetic field to give Lorentz forces that oppose the flow and detach the [[Bow shock (aerodynamics)|bow shock wave]] further ahead of the vehicle, lowering the [[heat flux]] which is due to the brutal recompression of air behind the [[stagnation point]]. Such passive [[Flow control (fluid)|flow control]] studies are still ongoing, but a large-scale demonstrator has yet to be built.<ref name="NASA reentry">{{cite report
 |last1=Sterkin |first1=Carol K.
 |date=December 1965
 |title=Interactions of spacecraft and other moving bodies with natural plasmas
 |id=19660007777. NASA-CR-70362. JPLAI/LS-541
 |publisher=NASA
 |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660007777.pdf
 }}</ref><ref name="ESA">{{cite web
 |author=<!--Not stated-->
 |title=Magnetohydrodynamic flow control during reentry
 |website=European Space Agency
 |url=https://www.esa.int/gsp/ACT/pro/projects/mhd_reentry.html
 |access-date=2018-04-13
}}</ref>

====Active flow control====
Active flow control by MHD force fields on the contrary involves a direct and imperious action of forces to locally accelerate or slow down the [[airflow]], modifying its velocity, direction, pressure, friction, heat flux parameters, in order to preserve materials and engines from stress, allowing [[hypersonic flight]]. It is a field of magnetohydrodynamics also called '''magnetogasdynamics''', '''magnetoaerodynamics''' or '''magnetoplasma aerodynamics''', as the working fluid is the air (a gas instead of a liquid) ionized to become electrically conductive (a plasma).

Air ionization is achieved at high altitude (electrical conductivity of air increases as atmospheric pressure reduces according to [[Paschen's law]]) using various techniques: [[high voltage]] [[Electric arc|electric arc discharge]], [[Radio frequency|RF]] ([[microwave]]s) electromagnetic [[glow discharge]], [[laser]], [[Cathode ray|e-beam]] or [[betatron]], [[radioactive source]]... with or without seeding of low [[ionization energy|ionization potential]] [[alkali]] substances (like [[caesium]]) into the flow.<ref name="Froning 1999">{{cite conference
 |last1=Froning |first1=H. D.
 |last2=Roach |first2=R. L.
 |date=November 1999
 |title=Influence of EM discharges on hypersonic vehicle lift, drag, and airbreathing thrust
 |conference=9th International Space Planes and Hypersonic Systems and Technologies Conference
 |location=Norfolk, VA
 |book-title=AIAA-99-4878
 |doi=10.2514/6.1999-487
 |url=http://ayuba.fr/pdf/ajax/froning1999.pdf
 }}</ref><ref name="Lineberry 2000">{{cite conference
 |last1=Lineberry |first1=John T.
 |last2=Rosa |first2=R. J.
 |last3=Bityurin |first3=V. A.
 |last4=Botcharov |first4=A. N.
 |last5=Potebnya |first5=V. G.
 |date=July 2000
 |title=Prospects of MHD flow control for hypersonics
 |conference=35th Intersociety Energy Conversion Engineering Conference and Exhibit
 |location=Las Vegas, NV
 |book-title=AIAA 2000-3057
 |doi=10.2514/6.2000-3057 
 |url=http://ayuba.fr/pdf/ajax/lineberry2000.pdf
 }}</ref>

MHD studies applied to [[aeronautics]] try to extend the domain of hypersonic [[Fixed-wing aircraft|planes]] to higher Mach regimes: 
* Action on the boundary layer to prevent laminar flow from becoming turbulent.<ref name="Ullah2021">{{cite journal 
 | last1 = Ullah | first1 = L.
 | last2 = Samad | first2 = A.
 | last3 = Nawaz | first3 = A.
 | date = 2021
 | title = The convective instability of the boundary-layer flow over a rotating cone in and out of a uniform magnetic field
 | journal = European Journal of Mechanics B/Fluids
 | volume = 87
 | pages = 12–23
 | doi = 10.1016/j.euromechflu.2020.12.013
 | bibcode = 2021EuJMB..87...12U
 | url = https://doi.org/10.1016/j.euromechflu.2020.12.013
 }}</ref>
* Shock wave mitigation for thermal control and reduction of the wave drag and form drag. Some theoretical studies suggest the flow velocity could be controlled everywhere on the wetted area of an aircraft, so shock waves could be totally cancelled when using enough power.<ref name="Petit 1983">{{cite conference
 | last1 = Petit |first1 = J.-P.
 |author-link1=Jean-Pierre Petit
 | date = September 1983
 | title = Is supersonic flight without shock wave possible?
 | conference = 8th International Conference on MHD Electrical Power Generation
 | location = Moscow, Russia
 | url = http://www.jp-petit.org/papers/MHD/1983-Moscow-shockwave.pdf
 }}</ref><ref name="Petit 1989a">
{{cite journal 
 | last1 = Petit | first1 = J.-P.
 | last2 = Lebrun | first2 = B.
 | date = 1989 
 | title = Shock wave annihilation by MHD action in supersonic flow. Quasi one dimensional steady analysis and thermal blockage
 | journal = European Journal of Mechanics B
 | series = B/Fluids
 | volume = 8
 | issue = 2
 | pages = 163–178
 | url = http://www.jp-petit.org/papers/MHD/1989-EurJMech-2.pdf
 }}
</ref><ref name="Petit 1989b">
{{cite journal 
 | last1 = Petit | first1 = J.-P.
 | last2 = Lebrun | first2 = B.
 | date = 1989 
 | title = Shock wave annihilation by MHD action in supersonic flows. Two-dimensional steady non-isentropic analysis. Anti-shock criterion, and shock tube simulations for isentropic flows
 | journal = European Journal of Mechanics B
 | series = B/Fluids
 | volume = 8
 | issue = 4
 | pages = 307–326
 | bibcode = 1989EuJMB...8..307L
 | url = http://www.jp-petit.org/papers/MHD/1989-EurJMech-2.pdf
 }}
</ref>
* Inlet flow control.<ref name="Lineberry 2000" /><ref name="Sheikin 2005">{{cite conference
 |last1=Sheikin |first1=Evgeniy G.
 |last2=Kuranov |first2=Alexander L.
 |date=2005
 |title=Scramjet with MHD Controlled Inlet
 |conference=AIAA/CIRA 13th International Space Planes and Hypersonics Systems and Technologies Conference
 |location=Capua, Italy
 |book-title=AIAA 2005-3223
 |doi=10.2514/6.2005-3223 
 |url=http://ayuba.fr/pdf/ajax/sheikin2005.pdf
 }}</ref><ref name="Petit 2008">{{Cite journal 
 |last1=Petit |first1=J.-P.
 |last2=Geffray |first2=J.
 |title=MHD flow-control for hypersonic flight
 |date=June 2009
 |journal=Acta Physica Polonica A
 |volume=115
 |issue=6
 |pages=1149–1513
 |doi=10.12693/aphyspola.115.1149
 |bibcode=2009AcPPA.115.1149P
 |url=http://przyrbwn.icm.edu.pl/APP/PDF/115/a115z667.pdf
 |doi-access=free
 }}</ref>
* Airflow velocity reduction upstream to feed a scramjet by the use of an MHD generator section combined with an MHD accelerator downstream at the exhaust nozzle, powered by the generator through an MHD bypass system.<ref name="Bityurin 1996">{{cite conference
 |last1=Bityurin |first1=V. A.
 |last2=Zeigarnik |first2=V. A.
 |last3=Kuranov |first3=A. L.
 |date=June 1996
 |title=On a perspective of MHD technology in aerospace applications
 |conference=27th Plasma Dynamics and Lasers Conference
 |location=New Orleans, LA
 |url=https://www.researchgate.net/publication/271369148
 |format=PDF 
 |doi=10.2514/6.1996-2355
}}</ref><ref name="Bityurin 1997">{{cite conference
 |last1=Bityurin |first1=V. A.
 |last2=Lineberry |first2=J.
 |last3=Potebnia |first3=V.
 |last4=Alferov |first4=V.
 |last5=Kuranov |first5=A.
 |last6=Sheikin |first6=E. G.
 |date=June 1997
 |title=Assessment of hypersonic MHD concepts
 |conference=28th Plasmadynamics and Lasers Conference
 |location=Atlanta, GA
 |doi=10.2514/6.1997-2393
 |url=http://ayuba.fr/pdf/ajax/bityurin1997.pdf
 }}</ref><ref name="Fraishtadt 1998">{{cite journal
 |last1=Fraĭshtadt |first1=V. L.
 |last2= Kuranov |first2=A. L.
 |last3=Sheĭkin |first3=E. G.
 |date=November 1998
 |title=Use of MHD systems in hypersonic aircraft
 |journal=Technical Physics
 |volume=43
 |issue=11
 |pages=1309–1313
 |doi=10.1134/1.1259189
 |url=http://ayuba.fr/pdf/ajax/fraishtadt1998.pdf
 |bibcode=1998JTePh..43.1309F|s2cid=122017083
 }}</ref><ref name="Sheikin 2003">{{cite conference
 |last1=Sheikin |first1=E. G.
 |last2=Kuranov |first2=A. L.
 |date=October 2003
 |title=Analysis of Scramjet with MHD bypass
 |conference=3rd workshop on Thermochemical processes in plasma aerodynamics
 |location=Saint Petersburg, Russia
 |s2cid=10143742
 |url=https://pdfs.semanticscholar.org/925b/e7242750df9e92a7d39fc4248826da59ff5f.pdf |archive-url=https://web.archive.org/web/20180412082744/https://pdfs.semanticscholar.org/925b/e7242750df9e92a7d39fc4248826da59ff5f.pdf |url-status=dead |archive-date=2018-04-12 }}</ref>

The Russian project [[Ayaks]] (Ajax) is an example of MHD-controlled hypersonic aircraft concept.<ref name="NAB" /> A US program also exists to design a hypersonic MHD bypass system, the [[Hypersonic Vehicle Electric Power System]] (HVEPS). A working prototype was completed in 2017 under development by [[General Atomics]] and the [[University of Tennessee Space Institute]], sponsored by the US [[Air Force Research Laboratory]].<ref name="General Atomics">{{cite web
 |author=<!--Not stated-->
 |date=21 March 2017
 |title=General Atomics Scores Power Production First
 |website=General Atomics
 |url=http://www.ga.com/general-atomics-scores-power-production-first
 |access-date=2018-04-13
}}</ref><ref name="UTSI">{{cite web
 |last1=Whorton |first1=Mark
 |date=2 July 2017
 |title=Hypersonic Vehicle Electric Power System (HVEPS)
 |website=The University of Tennessee Space Institute
 |url=http://www.utsi.edu/hypersonic-vehicle-electric-power-system/
 |access-date=2018-04-13
}}</ref><ref name="AFRL">{{cite web
 |author=<!--Not stated-->
 |date=7 June 2017
 |title=Scramjet MHD System Generates Electrical Power
 |website=Wright-Patterson Air Force Base
 |url=https://www.wpafb.af.mil/News/Article-Display/Article/401319/scramjet-mhd-system-generates-electrical-power/
 |access-date=2018-04-13
}}</ref> These projects aim to develop MHD generators feeding MHD accelerators for a new generation of high-speed vehicles. Such MHD bypass systems are often designed around a [[scramjet]] engine, but easier to design [[turbojet]]s are also considered,<ref name="Adamovich 2003">{{cite conference
 |last1=Adamovich |first1=Igor V.
 |last2=Rich |first2=J. William
 |last3=Schneider |first3=Steven J.
 |last4=Blankson |first4=Isaiah M.
 |date=June 2003
 |title=Magnetogasdynamic Power Extraction and Flow Conditioning for a Gas Turbine
 |conference=34th AIAA Plasmadynamics and Lasers Conference
 |location=Orlando, Florida
 |book-title=AIAA 2003-4289
 |doi=10.2514/6.2003-4289
 |url=http://ayuba.fr/pdf/ajax/adamovich2003.pdf
 }}</ref><ref name="Blankson 2003">{{cite conference
 |last1=Blankson |first1=Isaiah M.
 |last2=Schneider |first2=Stephen J.
 |date=December 2003
 |title=Hypersonic Engine using MHD Energy Bypass with a Conventional Turbojet
 |conference=12th AIAA International Space Planes and Hypersonic Systems and Technologies
 |location=Norfolk, Virginia
 |book-title=AIAA 2003-6922
 |doi=10.2514/6.2003-6922 
 |url=http://ayuba.fr/pdf/ajax/blankson2003.pdf
 }}</ref><ref name="Schneider 2011">{{cite conference
 |last1=Schneider |first1=Stephen J.
 |title=Annular MHD Physics for Turbojet Energy Bypas
 |conference=17th AIAA International Space Planes and Hypersonic Systems and Technologies Conference
 |location=San Francisco, California
 |book-title=AIAA–2011–2230
 |doi=10.2514/6.2011-2230
 |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110016528.pdf
 |hdl=2060/20110016528
 |hdl-access=free
 }}</ref> as well as subsonic [[ramjet]]s.<ref name="Chase 1998">{{cite conference
 |last1=Chase |first1=R. L.
 |last2=Boyd |first2=R.
 |last3=Czysz |first3=P.
 |last4=Froning, Jr. |first4=H. D.
 |last5=Lewis |first5=Mark
 |last6=McKinney |first6=L. E.
 |date=September 1998
 |title=An AJAX technology advanced SSTO design concept
 |conference=AIAA and SAE, 1998 World Aviation Conference 
 |book-title=Anaheim, CA
 |doi=10.2514/6.1998-5527
 |url=http://ayuba.fr/pdf/ajax/chase1998.pdf
 }}</ref>

Such studies covers a field of [[Magnetohydrodynamics#Ideal and resistive MHD|resistive MHD]] with [[magnetic Reynolds number]] ≪ 1 using [[Nonthermal plasma#Aerospace|nonthermal]] [[Degree of ionization#Physics usage|weakly ionized]] gases, making the development of demonstrators much more difficult to realize than for MHD in liquids. "Cold plasmas" with magnetic fields are subject to the [[electrothermal instability]] occurring at a critical Hall parameter, which makes full-scale developments difficult.<ref name="Park 2007">{{cite journal
 |last1=Park |first1=Chul
 |last2=Bogdanoff |first2=David W.
 |last3=Mehta |first3=Unmeel B.
 |date=July 2003
 |title=Theoretical Performance of a Magnetohydrodynamic-Bypass Scramjet Engine with Nonequilibrium Ionization
 |journal=Journal of Propulsion and Power
 |volume=19
 |issue=4
 |pages= 529–537
 |doi=10.2514/2.6156
 |url=http://ayuba.fr/pdf/ajax/park2003.pdf
 }}</ref>

==== Prospects ====
MHD propulsion has been considered as the main propulsion system for both marine and space ships since there is no need to produce lift to counter the [[gravity of Earth]] in water (due to [[buoyancy]]) nor in space (due to [[weightlessness]]), which is ruled out in the case of [[flight]] in the [[atmosphere]].

Nonetheless, considering the current problem of the [[Electric power|electric power source]] solved (for example with the availability of a still missing multi-megawatt compact [[Fusion power|fusion reactor]]), one could imagine future aircraft of a new kind silently powered by MHD accelerators, able to ionize and direct enough air downward to lift several [[tonne]]s. As external flow systems can control the flow over the whole wetted area, limiting thermal issues at high speeds, ambient air would be ionized and radially accelerated by Lorentz forces around an [[Rotational symmetry#Rotational symmetry with respect to any angle|axisymmetric]] body (shaped as a [[cylinder]], a [[cone]], a [[sphere]]...), the entire [[airframe]] being the engine. Lift and thrust would arise as a consequence of a [[pressure]] difference between the upper and lower surfaces, induced by the [[Coandă effect]].<ref name='"Coanda patent">{{cite patent
 |country=US
 |number=2108652
 |status=patent
 |title=Propelling device
 |pubdate=1936-01-15
 |gdate=1938-02-16
 |fdate=1936-01-10
 |url=https://patentimages.storage.googleapis.com/d9/67/6d/6cbdb5f33cc76e/US2108652.pdf
}}</ref><ref name="Coanda saucers">{{cite journal
 |last1=Petit |first1=J.-P.
 |date=August 1974
 |title=Flying saucers R&D: The Coanda effect (English version)
 |journal=Science & Vie
 |issue=683
 |pages=68–73
 |url=http://ayuba.fr/pdf/coanda_disc.pdf
 }}</ref> In order to maximize such pressure difference between the two opposite sides, and since the most efficient MHD converters (with a high [[Hall effect]]) are disk-shaped, such MHD aircraft would be preferably flattened to take the shape of a [[Lens (optics)#Types of simple lenses|biconvex lens]]. Having no [[wing]]s nor [[airbreathing jet engine]]s, it would share no similarities with conventional aircraft, but it would behave like a [[helicopter]] whose [[Helicopter rotor|rotor blades]] would have been replaced by a "purely electromagnetic rotor" with no moving part, sucking the air downward. Such concepts of flying MHD disks have been developed in the [[peer review]] literature from the mid 1970s mainly by physicists [[Leik Myrabo]] with the [[Lightcraft]],<ref name="Myrabo 1976">
{{cite journal
 | author = Myrabo, L.N.
 | author-link = Leik Myrabo
 | date = 1976
 | title = MHD propulsion by absorption of laser radiation
 | journal = Journal of Spacecraft and Rockets
 | volume = 13
 | issue = 8
 | url = http://ayuba.fr/pdf/myrabo1976.pdf
 | doi = 10.2514/3.27919
 | pages=466–472
 | bibcode = 1976JSpRo..13..466M
 }}</ref><ref name="Myrabo 1999">{{cite conference
 | last1 = Myrabo | first1 =  L. N.
 | last2 = Kerl | first2 = J.M.
 | display-authors=etal
 | date = June 1999
 | title = MHD slipstream accelerator investigation in the RPI hypersonic shock tunnel
 | conference = 35th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit
 | book-title = AIAA-1999-2842
 | location = Los Angeles, CA
 | url = http://ayuba.fr/pdf/myrabo1999.pdf
 | doi = 10.2514/6.1999-2842 
}}</ref><ref name="Myrabo 2000a">{{cite conference
 | last1 = Myrabo | first1 =  L. N.
 | display-authors=etal
 | date = January 2000
 | title = Experimental investigation of a 2-D MHD slipstream generator and accelerator with freestream Mach = 7.6 and T(0) = 4100 K
 | conference = 38th Aerospace Sciences Meeting and Exhibit 
 | book-title =  AIAA-00-0446
 | location = Reno, NV
 | url = http://ayuba.fr/pdf/myrabo2000a.pdf
 | doi = 10.2514/6.2000-446 
}}</ref><ref name="Myrabo 2000b">{{cite conference
 | last1 = Myrabo | first1 =  L. N.
 | display-authors=etal
 | date = July 2000
 | title = Experimental Investigation of a 2-D MHD Slipstream Accelerator and Generator
 | conference = 36th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit
 | book-title = AIAA-00-3486
 | location = Huntsville, AL
 | url = http://ayuba.fr/pdf/myrabo2000b.pdf
 | doi = 10.2514/6.2000-3486
}}</ref><ref name="Myrabo book">{{cite book
 |last1=Myrabo |first1=Leik N.
 |last2=Lewis |first2=John S.
 |title=Lightcraft Flight Handbook LTI-20: Hypersonic Flight Transport for an Era Beyond Oil
 |date=May 2009
 |publisher=Collector's Guide Publishing
 |isbn=978-1926592039
}}</ref> and [[Subrata Roy (scientist)|Subrata Roy]] with the [[Wingless Electromagnetic Air Vehicle]] (WEAV).<ref name="Roy 2011">{{cite report
 |last1=Roy |first1=Subrata
 |last2=Arnold |first2=David
 |last3=Lin |first3=Jenshan
 |last4=Schmidt |first4=Tony
 |last5=Lind |first5=Rick
 |last6=Durscher |first6=Ryan
 |last7=Riherd |first7=Mark
 |last8=Houba |first8=Tomas
 |last9=Anderson |first9=Richard
 |last10=Zito |first10=Justin
 |last11=Casanova |first11=Joaquin
 |last12=Thomson |first12=Carlton
 |last13=Blood |first13=Daniel
 |last14=Tran |first14=Dong
 |display-authors=5
 |date=20 December 2011
 |title=Demonstration of a Wingless Electromagnetic Air Vehicle
 |id=AFRL-OSR-VA-TR-2012-0922
 |publisher=Defense Technical Information Center
 |editor1=Air Force Office of Scientific Research
 |editor2=University of Florida
 |asin=B01IKW9SES
 |url=http://apps.dtic.mil/dtic/tr/fulltext/u2/a564120.pdf
 |archive-url=https://web.archive.org/web/20130517063830/http://www.dtic.mil/dtic/tr/fulltext/u2/a564120.pdf
 |url-status=live
 |archive-date=May 17, 2013
 }}</ref><ref name="Roy patent 2013">{{cite patent
| country = US
| number = 8382029
| status = patent
| title = Wingless hovering of micro air vehicle
| gdate = 2013-02-26
| fdate = 2008-12-23
| pridate = 2006-07-31
| invent1 = Subrata Roy 
| assign1 = University of Florida Research Foundation Inc
| url = https://patentimages.storage.googleapis.com/0b/a8/52/3c6718c040ad54/US8382029.pdf
}}</ref><ref name="Roy patent 2015">{{cite patent
| country = US
| number = 8960595
| status = patent
| title = Wingless hovering of micro air vehicle
| gdate = 2015-02-24
| fdate = 2012-12-19
| pridate = 2006-07-31
| invent1 = Subrata Roy 
| assign1 = University of Florida Research Foundation Inc.
| url = https://patentimages.storage.googleapis.com/25/43/bb/2bdc198ea976a9/US8960595.pdf
}}</ref>

These futuristic visions have been advertised in the media although they still remain beyond the reach of modern technology.<ref name="Science & Vie 1976">{{cite magazine
 |last1=Petit |first1=Jean-Pierre
 |title=Un moteur à plasma pour ovnis
 |trans-title=A plasma engine for UFOs
 |language=fr
 |date=March 1976
 |magazine=Science & Vie
 |issue=702
 |pages=42–49
 |url=http://ayuba.fr/pdf/S&V702-moteur_plasma_ovnis.pdf
 }}</ref><ref name="Popular Mechanics 1995" /><ref name="Scientific American">{{cite web
 |last1=Greenemeier |first1=Larry
 |date=7 July 2008
 |title=The World's First Flying Saucer: Made Right Here on Earth
 |website=Scientific American
 |url=https://www.scientificamerican.com/article/worlds-first-flying-saucer/
}}</ref>

===Spacecraft propulsion===

{{main|Plasma propulsion engine}}
{{See also|Magnetoplasmadynamic thruster|Pulsed inductive thruster}}
A number of experimental methods of [[spacecraft propulsion]] are based on magnetohydrodynamics. As this kind of MHD propulsion involves compressible fluids in the form of plasmas (ionized gases) it is also referred to as magnetogasdynamics or '''magnetoplasmadynamics'''.

In such [[Electrically powered spacecraft propulsion#Electromagnetic|electromagnetic thrusters]], the working fluid is most of the time ionized [[hydrazine]], [[xenon]] or [[lithium]]. Depending on the propellant used, it can be seeded with [[alkali]] such as [[potassium]] or [[caesium]] to improve its electrical conductivity. All charged species within the plasma, from positive and negative ions to free electrons, as well as neutral atoms by the effect of collisions, are accelerated in the same direction by the Lorentz "body" force, which results from the combination of a magnetic field with an orthogonal electric field (hence the name of "cross-field accelerator"), these fields not being in the direction of the acceleration. This is a fundamental difference with [[ion thruster]]s which rely on [[electrostatics]] to accelerate only positive ions using the [[Coulomb force]] along a [[high voltage]] electric field.

First experimental studies involving cross-field plasma accelerators (square channels and rocket nozzles) date back to the late 1950s. Such systems provide greater [[thrust]] and higher [[specific impulse]] than conventional [[Rocket engine#Terminology|chemical rockets]] and even modern ion drives, at the cost of a higher required energy density.<ref name="Resler 1958">{{cite journal
 |last1=Resler |first1=E.L.
 |last2=Sears |first2=W.R.
 |title=Magneto-Gasdynamic Channel Flow
 |date=1958
 |journal=Zeitschrift für Angewandte Mathematik und Physik
 |volume=9b
 |issue=5–6
 |pages=509–518
|doi=10.1007/BF02424770
 |bibcode=1958ZaMP....9..509R
 |s2cid=97266881
 }}</ref><ref name="Wilson 1958">{{cite book
 |last1=Wilson |first1=T.A.
 |chapter=Remarks on Rocket and Aerodynamic Applications of Magnetohydrodynamic Channel Flow
 |date=December 1958
 |publisher=Cornell University
 |title=TN-58-1058, ASTIA 207 228
}}</ref><ref name="Wood 1960">{{cite journal
 |last1=Wood |first1=G.P.
 |last2=Carter |first2=A.F.
 |title=Considerations in the Design of a Steady D.C. Plasma Generator
 |date=1960
 |journal=Dynamics of Conducting Gases (Proceedings of the 3rd Biennial Gas Dynamics Symposium)
 }}</ref><ref name="Kerrebrock 1960">{{cite journal
 |last1=Kerrebrock |first1=Jack L.
 |title=Electrode Boundary Layers in Direct-Current Plasma Accelerators
 |date=August 1961
 |journal=Journal of the Aerospace Sciences
 |volume=28
 |issue=8
 |pages=631–644
 |url=http://ayuba.fr/pdf/kerrebrock1961.pdf
 |doi=10.2514/8.9117
}}</ref><ref name="Oates 1962">{{cite journal
 |last1=Oates |first1=Gordon C.
 |title=Constant-Electric-Field and Constant-Magnetic-Field Magnetogasdynamic Channel Flow
 |date=1962
 |journal=Journal of the Aerospace Sciences
 |volume=29
 |issue=2
 |pages=231–232
 |doi=10.2514/8.9372
 |url=http://ayuba.fr/pdf/oates1962.pdf
 }}</ref><ref name="Rosciszewski 1965">{{cite journal 
 |last1=Rosciszewski |first1=Jan
 |title=Rocket motor with electric accelerationin tehthroat
 |date=March 1965
 |journal=Journal of Spacecraft and Rockets
 |volume=2
 |issue=2
 |pages=278–280
 |url=http://ayuba.fr/pdf/rosciszewski1965.pdf
 |doi=10.2514/3.28172
|bibcode=1965JSpRo...2..278R}}</ref>

Some devices also studied nowadays besides cross-field accelerators include the [[magnetoplasmadynamic thruster]] sometimes referred to as the Lorentz force accelerator (LFA), and the electrodeless [[pulsed inductive thruster]] (PIT).

Even today, these systems are not ready to be launched in space as they still lack a suitable compact power source offering enough [[energy density]] (such as hypothetical [[Fusion power|fusion reactors]]) to feed the power-greedy [[electromagnet]]s, especially pulsed inductive ones. The rapid ablation of electrodes under the intense thermal flow is also a concern. For these reasons, studies remain largely theoretical and experiments are still conducted in the laboratory, although over 60 years have passed since the first research in this kind of thrusters.

== Fiction ==
''Oregon,'' a ship in the ''[[Oregon Files]]'' series of books by author [[Clive Cussler]], has a magnetohydrodynamic drive. This allows the ship to turn very sharply and brake instantly, instead of gliding for a few miles. In ''[[Valhalla Rising (novel)|Valhalla Rising]],'' Clive Cussler writes the same drive into the powering of [[Captain Nemo]]'s ''[[Nautilus (Verne)|Nautilus]].''

The film adaptation of ''[[The Hunt for Red October (film)|The Hunt for Red October]]'' popularized the magnetohydrodynamic drive as a "caterpillar drive" for [[submarine]]s, a nearly undetectable "silent drive" intended to achieve [[Stealth technology#Acoustics|stealth]] in [[submarine warfare]]. In reality, the current traveling through the water would create gases and noise, and the magnetic fields would induce a detectable magnetic signature. In the film, it was suggested that this sound could be confused with geological activity. In [[The Hunt for Red October|the novel]] from which the film was adapted, the caterpillar that ''Red October'' used was actually a [[pump-jet]] of the so-called "tunnel drive" type (the tunnels provided acoustic camouflage for the cavitation from the propellers).

In the [[Ben Bova]] novel ''[[The Precipice (Bova novel)|The Precipice]],'' the ship where some of the action took place, ''Starpower 1,'' built to prove that exploration and mining of the [[asteroid belt]] was feasible and potentially profitable, had a magnetohydrodynamic drive mated to a [[fusion power]] plant.

== See also ==
* [[Electrohydrodynamics]]
* [[Lorentz force]], relates electric and magnetic fields to propulsion force

==References==
{{reflist}}
{{refbegin}}
{{refend}}

==External links==
* [http://www.evilmadscientist.com/article.php/SimpleMHD Demonstrate Magnetohydrodynamic Propulsion in a Minute]

{{DEFAULTSORT:Magnetohydrodynamic Drive}}
[[Category:Marine propulsion]]
[[Category:Fluid dynamics]]
[[Category:Plasma technology and applications]]
[[Category:Magnetic propulsion devices]]