Chapter 3 Basic Plasma Physics - NASA

37 Chapter 3 Basic Plasma Physics Introduction Electric propulsion achieves high specific impulse by the acceleration of charged particles to high velocity. The charged particles are produced by ionization of a propellant gas, which creates both ions and electrons and forms what is called a Plasma . Plasma is then a collection of the various charged particles that are free to move in response to fields they generate or fields that are applied to the collection and, on the average, is almost electrically neutral. This means that the ion and electron densities are nearly equal, ni ne, a condition commonly termed quasi-neutrality. This condition exists throughout the volume of the ionized gas except close to the boundaries, and the assumption of quasi-neutrality is valid whenever the spatial scale length of the Plasma is much larger than the characteristic length over which charges or boundaries are electrostatically shielded, called the Debye length.

respectively. Note that and J comprise all the charges and currents for all the particle species that are present in the plasma, including multiply charged ions. The charge density is then = qsns = eZn() i ne s , (3.2-5) where qs is the charge state of species s, Z is the charge state, ni is the ion number density, and ne is the electron number ...

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