Electrodeless Plasma Thruster
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The electrodeless plasma thruster is a
spacecraft propulsion Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. In-space propulsion exclusively deals with propulsion systems used in the vacuum of space and should not be confused with space launch or atmospheric e ...
engine commercialized under the acronym "E-IMPAcT" for "Electrodeless-Ionization Magnetized Ponderomotive Acceleration Thruster". It was created by Gregory Emsellem, based on technology developed by French Atomic Energy Commission scientist Dr Richard Geller and Dr. Terenzio Consoli, for high speed plasma beam production. The
electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...
less plasma thruster was developed and adapted to various spacecraft propulsion needs b
The Elwing Company
between 2002 and 2015.


Operating principle

#
Propellant A propellant (or propellent) is a mass that is expelled or expanded in such a way as to create a thrust or another motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicle ...
is injected at the upstream side of the thruster body. In cases where the propellant used is not gaseous (e.g.,
alkali metal The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...
s) at the local temperature, the propellant must be vaporized. # Gaseous propellant is ionized by one of the following methods: #* bombarding the propellant with
electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...
s emitted by a
hot cathode In vacuum tubes and gas-filled tubes, a hot cathode or thermionic cathode is a cathode electrode which is heated to make it emit electrons due to thermionic emission. This is in contrast to a cold cathode, which does not have a heating element ...
or by an
electron gun file:Egun.jpg, Electron gun from a cathode-ray tube file:Vidicon Electron Gun.jpg, The electron gun from an RCA Vidicon video camera tube An electron gun (also called electron emitter) is an electrical component in some vacuum tubes that produc ...
. #* a steady state
electrical discharge In electromagnetism, an electric discharge is the release and transmission of electricity in an applied electric field through a medium such as a gas (i.e., an outgoing flow of electric current through a non-metal medium).American Geophysical U ...
between two electrodes. #* applying an alternating electric field either via a capacitive discharge or an inductive discharge or even a helicon discharge. #*
electromagnetic wave In physics, electromagnetic radiation (EMR) is a self-propagating wave of the electromagnetic field that carries momentum and radiant energy through space. It encompasses a broad spectrum, classified by frequency or its inverse, wavelength, ...
s of various frequency from
radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the u ...
up to
gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...
s, which is especially useful for solid propellant in which case the propellant can be simultaneously vaporized and ionized by a
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...
impulse. #As the ionization stage is subjected to a steady
magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...
, the ionization process can use one of the numerous resonances existing in magnetized plasma, such as
ion cyclotron resonance Ion cyclotron resonance is a phenomenon related to the movement of ions in a magnetic field. It is used for accelerating ions in a cyclotron, and for measuring the masses of an ionized analyte in mass spectrometry, particularly with Fourier transfor ...
(ICR),
electron cyclotron resonance Electron cyclotron resonance (ECR) is a phenomenon observed in plasma physics, condensed matter physics, and accelerator physics. It happens when the frequency of incident radiation coincides with the natural frequency of rotation of electrons in ...
(ECR) or
lower hybrid oscillation Lower may refer to: * ''Lower'' (album), 2025 album by Benjamin Booker * Lower (surname) * Lower Township, New Jersey *Lower Receiver (firearms) In firearms terminology and law, the firearm frame or receiver is the part of a firearm which integr ...
, to produce a high density
cold plasma Cold is the presence of low temperature, especially in the atmosphere. In common usage, cold is often a subjective perception. A lower bound to temperature is absolute zero, defined as 0.00K on the Kelvin scale, an absolute thermodynamic ...
. # The cold and dense plasma, produced by the ionization stage, then drifts toward the acceleration stage by diffusion across a region of higher magnetic field intensity. # In the acceleration stage the propellant plasma is accelerated by magnetized
ponderomotive force In physics, a ponderomotive force is an nonlinear force that a charged particle experiences in an inhomogeneous oscillating electromagnetic field. It causes the particle to move towards the area of the weaker field strength, rather than oscillati ...
in an area where both non-uniform static magnetic fields and non-uniform high-frequency electromagnetic fields are applied simultaneously.


Advantages

This thruster technology can deliver large thrust density as the acceleration process is not limited by plasma density through Hall Parameter or grid electrical screening. Further, as the ponderomotive force accelerates all plasma species in the same direction, this thruster technology does not need any neutralizer. The fact that electrodeless plasma thruster is inherently multi-staged allows it to optimize both stages independently, or to throttle the thruster at constant power between higher
specific impulse Specific impulse (usually abbreviated ) is a measure of how efficiently a reaction mass engine, such as a rocket engine, rocket using propellant or a jet engine using fuel, generates thrust. In general, this is a ratio of the ''Impulse (physics), ...
and higher
thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...
. The field of ponderomotive force is created by a non-uniform high frequency field and static magnetic field, thus it implies no grids nor contact between the plasma and any electrodes, hence it avoids most thruster erosion and spacecraft contamination issues.


Applications

Propulsion systems based on electrodeless plasma thrusters seem ideally suited for orbit raising for large
geostationary satellite A geostationary orbit, also referred to as a geosynchronous equatorial orbit''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources. (GEO), is a circular geosynchronous orbit in altitud ...
s, and would also be able to perform orbital stationkeeping, hence enabling important propellant mass savings. The ability of this technology to provide large thrust density also allows faster missions to the outer planets.


Other research on the same phenomenon

The use of
ponderomotive force In physics, a ponderomotive force is an nonlinear force that a charged particle experiences in an inhomogeneous oscillating electromagnetic field. It causes the particle to move towards the area of the weaker field strength, rather than oscillati ...
to accelerate a plasma has recently been investigated from a theoretical point of view by
Princeton Plasma Physics Laboratory Princeton Plasma Physics Laboratory (PPPL) is a United States Department of Energy national laboratory for plasma physics and nuclear fusion science. Its primary mission is research into and development of fusion as an energy source. It is know ...
scientists I. Y. Dodin, Y. Raitses and N. J. Fisch.Princeton Plasma Physics Laboratory publications http://htx.pppl.gov/publications.html Some theoretical research has also been reported around the debated issue of the existence of a double layer in such a thruster, even if such a double layer structure would be current-free, as both ions and electrons travel in the same direction at the same average terminal speed. The existence of current free double layer is still debated among plasma physicists.


See also

* Electrodeless plasma excitation *
Electrodeless lamp The induction lamp, electrodeless lamp, or electrodeless induction lamp is a gas-discharge lamp in which an electric or magnetic field transfers the power required to generate light from outside the lamp envelope to the gas inside. This is in co ...


References


External links


AIAA paper on this technology


{{spacecraft propulsion Ion engines Spacecraft components