Plasma has lured the attention of physicists towards itself for quite some time now. 99% of the universe is made up of plasma. It is the purest form of raw and intense energy which possesses all the types of matter known to mankind. Scientists have come up with various theories and technologies to harness this versatile source of energy. The “plasma propulsion” is a technology which harnesses plasma to achieve vehicular propulsion, mostly spacecrafts. This technology is gaining importance due to the depletion of conventional sources of energy such as fossil fuels which are used to fuel vehicles for transportation. This paper showcases the ideology of plasma and its types. Further, this article also deals with the types of plasma propulsion systems, their architecture, working, pros and cons, and the types of propellants used in ion thrusters. This paper also houses a brief description of various missions which have incorporated ion thrusters. And towards the fag end of this article, a vision of “terrestrial transportation” has also been idealized followed by the list of references.

1. ION THRUSTERS
AN APPLICATION OF PLASMA PHYSICS
By
Bhushith. M. Kumar
Under the guidance of
Dr. A. D. Srinivasan

2. PLASMA….. WHAT’S THAT ?
 Plasma is loosely described as an
electrically neutral medium of
unbound positive and negative
particles.
 Plasma is the most abundant form of
ordinary matter in the universe.
Mostly in the intergalactic regions and
near neutron stars.
 There are two types of plasma –
thermal and non-thermal plasma
 In a high pressure gas discharge the
collision between electrons and gas
molecules occurs frequently. This
causes thermal equilibrium between
the electrons and gas molecules. These
are thermal plasma.
 A “non-thermal plasma” is one in which
the thermal motion of the ions can be
ignored.
 There are several means for generation
of plasma; however, one principle is
common to all of them: there must be
energy input to produce and sustain
it. For this case, plasma is generated
when an electrical current is applied
across a dielectric gas or fluid.
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3. ION THRUSTERS – NOT A SCI-FI ANYMORE
 An ion thruster is a form of electric
propulsion used for spacecraft
propulsion that creates thrust by
accelerating ions.
 Ion thrusters have input power spanning
1 to 7 kilowatts, exhaust velocity 20 to
50 kilometers per second, thrust 20 to
250 milli Newton and efficiency 60% to
80%.
 Applications include control of the
orientation and position of
orbiting satellites (some satellites have
dozens of low-power ion thrusters) and
use as a main propulsion engine for
low-mass robotic space vehicles (for
example Deep Space 1 and Dawn).
 The first person to publish mention of the
idea of plasma engine was Konstantin
Tsiolkovsky in 1911.
 A working ion thruster was built by Harold
R. Kaufman in 1959 at the NASA Glenn
Research Center facilities.
 Until the 1990s they were mainly used for
satellite stabilization in North-South and
in East-West directions. Some 100–200
engines completed their mission on
Soviet and Russian satellites until the late
1990s.
 Soviet thruster design was introduced to
the West in 1992 after a team of electric
propulsion specialists, under the support
of the Ballistic Missile Defense
Organization, visited Soviet laboratories.
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4. THE IDEOLOGY BEHIND ION THRUSTERS
 Ion thrusters use beams
of ions (electrically charged atoms
or molecules) to create thrust in
accordance with momentum
conservation. The method of
accelerating the ions varies, but all
designs take advantage of
the charge/mass ratio of the ions.
 This ratio means that relatively
small potential differences can
create very high exhaust velocities.
This reduces the amount
of reaction mass or fuel required.
 The drawback of ion thrusters is low
spacecraft acceleration and hence
unsuited for launching spacecraft
into orbit, but they are ideal for in-
space propulsion applications.
 There are two types of ion thrusters
based on how ions are accelerated.
They are – Electrostatic and
electromagnetic ion thrusters.
 Electric power supplies for ion thrusters
are usually solar panels but, at
sufficiently large distances from the
Sun, nuclear power is used.
 Thrust = 2*η*power/ (g * Isp)
Where,
Thrust is the force in N
η is the efficiency, a dimensionless
value between 0 and 1
Power is the electrical energy input
to the thruster in W
g is a constant, the acceleration due
to gravity 9.81 m/s2
Isp is the Specific impulse in s
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5. ELECTROSTATIC ION THRUSTERS:
GRIDDED ION THRUSTERS
Gridded electrostatic
thrusters commonly
utilize xenon gas. This
gas has no charge
and is ionized by
bombarding it with
energetic electrons.
 Ion thrusters emit a
beam of positive
charged xenon ions
only. To avoid charging
up the spacecraft,
another cathode is
placed near the
engine, which emits
electrons (basically
the electron current is
the same as the ion
current) into the ion
beam. This also
prevents the beam of
ions from returning to
the spacecraft and
cancelling the thrust.
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7. HALL EFFECT THRUSTERS
Hall effect
thrusters accelerate
ions with the use of
an electric potential
maintained between
a cylindrical anode
and negatively
charged plasma that
forms the cathode.
The bulk of the
propellant
(typically xenon gas)
is introduced near
the anode, where it
becomes ionized,
and the ions are
attracted towards the
cathode; they
accelerate towards
and through it,
picking up electrons
as they leave to
neutralize the beam
and leave the
thruster at high
velocity
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9. ELECTROMAGNETIC THRUSTERS
PULSE INDUCTIVE THRUSTERS LITHIUM LORENTZ FORCE (LI-LFA)
 Pulsed inductive thrusters (PIT) use
pulses of thrust instead of one
continuous thrust, and have the ability
to run on power levels in the order of
Megawatts (MW).
 PITs consist of a large coil encircling a
cone shaped tube that emits the
propellant gas. Ammonia is the gas
commonly used in PIT engines.
 For each pulse of thrust the PIT gives,
a large charge first builds up in a group
of capacitors behind the coil and is
then released.
 Hydrogen, argon, ammonia,
and nitrogen gas can be used as
propellant here.
 The gas first enters the main chamber
where it is ionized into plasma by the
electric field between the anode and
the cathode. This plasma then
conducts electricity between the
anode and the cathode.
 This new current creates a magnetic
field around the cathode, which
crosses with the electric field, thereby
accelerating the plasma due to the
Lorentz force and exits out of the
nozzle.
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10. ADVANCED ION THRUSTERS:
ELECTRODELESS PLASMA THRUSTERS
 Electrodeless plasma thrusters have two unique
features: the removal of the anode and cathode
electrodes and the ability to throttle the engine.
 The removal of the electrodes takes away the factor of
erosion, which limits lifetime on other ion engines.
 Neutral gas is first ionized by electromagnetic waves and
then transferred to another chamber where it is
accelerated by an oscillating electric and magnetic field,
also known as the ponderomotive force.
 This separation of the ionization and acceleration stage
gives the engine the ability to throttle the speed of
propellant flow, which then changes the thrust
magnitude and specific impulse values.
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11. PROPELLANTS ENERGY EFFICIENCY
 The ideal propellant for ion drives is
thus a propellant molecule or atom
that is easy to ionize.
 Older designs used mercury, but this is
toxic and expensive, tended to
contaminate the vehicle with the metal
and was difficult to feed accurately.
 Many current designs use xenon gas,
as it is easy to ionize, has a reasonably
high atomic number, its inert nature,
and low erosion. However, xenon is
globally in short supply and very
expensive.
 VASMIR engines can use any material
as propellant and is under
development and its success could be
greatest invention this era.
 The actual overall system energy
efficiency in use is determined by
the propulsive efficiency, which
depends on vehicle speed and exhaust
speed. Some thrusters can vary
exhaust speed in operation.
 Optimal efficiencies and exhaust
velocities can thus be calculated for
any given mission to give minimum
overall cost.
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As of now, plasma propulsion is only used in space
applications. But, in the near future, assuming the
development in the field of plasma propulsion to be
prominent, terrestrial vacuum tubes can be set up connecting
two places inside which a train runs using “ion thrusters”.
This sort of transportation system can also be used by miners
and for deep ocean expeditions.
FAMOUS MISSIONS:
•SERT
•Deep Space 1
•Hayabusa