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This Defense Intelligence Agency reference document, dated 1 November 2010, is one of a series of advanced technology reports produced in FY 2010 under the Advanced Aerospace Weapons System Applications (AAWSA) Program. It covers fusion plasma physics, confinement methods, and propulsion concepts that use aneutronic fuels such as hydrogen and boron-11. It concludes that such thrusters may soon replace satellite ion thrusters. It also finds that they will not be practical beyond the solar system without breakthrough propulsion physics.
UNCLASSIFIED/ /l"e" Cl"l"!e1,it tl!!L CHE I ION PROPULSION Ion propulsion is a method by which the principles of electromagnetics are exploited to accelerate an ionized gas in a controlled manner. The forces involved to accelerate the plasma, by Newton's third law, act to propel an object such as a rocket or spacecraft along a given path. The classification of the different plasma propulsion designs is somewhat difficult. Some designs involve electrostatic fields only, some use magnetic fields for ionization purposes but not for ion acceleration, and some designs use both electric and magnetic fields for ion acceleration and thrust. In addition, some designs emit ions from a material anode, while other designs use electric and magnetic fields to ionize a gas by one of several methods, for example, by enhancing collisions or by using radiofrequency (RF) waves, to create a plasma. The different classes of plasma propulsion are described in the following subsections. The use of fusion reactions in an ion propulsion device could significantly enhance the energy of the accelerated ions augmenting the net thrust per watt expended. We will examine the methods of plasma ion propulsion that may benefit from aneutronic fusion. Ion Thrusters Ion thrusters typically emit charged particles from an anode or cathode to create an ion population. This population is then accelerated by an electric (and sometimes magnetic) field to generate thrust. Examples of ion thrusters include gridded electrostatic thrusters, Hall effect thrusters, and field-emission electric propulsion systems: Gridded Electrostatic Thrusters. Gridded electrostatic thrusters were originally derived from a duoplasmatron design (which uses electrons from a cathode filament to ionize an introduced gas). Such designs then accelerate and focus ions into a beam, using an electrostatic potential, with a force equal to the ion mass times the strength of the electric field (Coulomb force). An external (to the plasma chamber) electron gun expels electrons into the exhaust to neutralize the system (to keep the spacecraft from charging up, pulling the ions [exhaust] back toward the spacecraft and lowering efficiency dramatically). These designs are typically low thrust and low specific impulse (lsp). Hall Effect Thruster. Hall thrusters use a magnetic field to trap electrons (which are used to ionize the gas) and use an electric field to accelerate ions to create thrust. The electrons also form a virtual cathode, in place of a physical grid, which is used to accelerate the ions. Lastly, electrons are used to neutralize the exhaust. About 30 percent of the discharge current is an electron current, which does not produce thrust. This limits the energetic efficiency of the Hall effect thruster. This design can produce a specific impulse of ~1,500 seconds and thrusts of several tens of mN up to ~3 N. Field-Emission Electric Propulsion Systems. A field-emission electric propulsion (FEEP) system uses a very strong electric field to cause metal ions to be emitted from a metal tip. These ions are then electrostatically accelerated to provide thrust. An electron gun neutralizes the exhaust. This is typically a very-low-thrust system. PLASMA THRUSTER Plasma thruster designs usually ionize a gas contained within a chamber, which is then accelerated using electric and magnetic forces (Lorentz force). Examples of plasma thruster designs discussed in the following subsections include magnetoplasmadynamic and Lithium Lorentz Force Accelerator (LiLFA) thrusters, electrodeless thrusters, helicon 14 UNCLASSIFIED//Flilll. lilFFUil,t.k l.lli&i lil'lk>/
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Report, from the dia collection. The PDF is mirrored here; the original link is above. 36 pages are in the text index: search them above, or from the library's search.