Conventional thrusters are based on chemical reactions. The particle bulk velocity at the exit of the nozzle is restricted to a few km/s. To transfer higher momentum to the payload, more propellent has to be employed.
An ion thruster uses an electrostatic field rather than a chemical process to accelerate the particles. Reachable ion velocities are up to 100 km/s. In comparison with a conventional thruster, an ion thruster is capable of transferring the same momentum with up to two orders of magnitude less propellent.
The ion thruster was first used in deep space during the DS1 mission .
A full particle code , in which ions as well as electrons are described completely kinetically, was developed to model the interaction of the thruster plasma and the ambient plasma.
Strong divergence (mpg, 1.0 MB)
Weak divergence (mpg, 1.2 MB)
The animations show the the dynamics of the electrons and ions. The divergence of the ion beam is strongly influenced by the neutralization by the electrons. The left-hand figure shows a situation with poor neutralization; the right-hand figure illustrates optimal neutralization, which results in a weak beam divergence. For further details, please see Carsten Othmer's Numerische Simulation extraterrestrischer Plasmen site.
References
Othmer, C., K. H. Glassmeier, U. Motschmann, J. Schüle, Ch. Frick, Three-dimensional simulations of ion thruster beam neutralisation, Physics of Plasmas, 7, 5242-5251, 2000.
Othmer, C., K. H. Glassmeier, U. Motschmann, J. Schüle, Ch. Frick, Numerical Simulation of ion thruster‑induced plasma dynamics, Adv. Space Res., 29(9), 1357-1362, 2002.
Othmer, C., K. H. Glassmeier, U. Motschmann, I. Richter, Numerical parameter studies of ion thruster beam neutralization, J. of Propulsion and Power, 19, 953-963, 2003.