ION THRUSTERS (an application of plasma physics) ppt
- 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. 6/9/2015Ion Thrusters 2
- 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. 6/9/2015Ion Thrusters 3
- 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 6/9/2015Ion Thrusters 4
- 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. 6/9/2015Ion Thrusters 5
- 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 6/9/2015Ion Thrusters 7
- 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. 6/9/2015Ion Thrusters 9
- 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. 6/9/2015Ion Thrusters 10
- 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. 6/9/2015Ion Thrusters 11
- 12. 6/9/2015Ion Thrusters 12 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