Conventionally speaking, rocketry requires a body of 80-90% fuel in order to achieve a thrust/weight ratio duration capable of putting an object into orbit, and then even more to get them to destination, making them very fuel inefficient with most of a rocket being taken up by its fuel stores.
“Electric thrusters” or plasma-rockets are a fuel ultra-efficient method of applying thrust. They work using the ionized nature of the thrust itself and an acceleration assembly similar to that of a railgun to impart additional velocity upon the plasma, as well as its own already very high thermal/compression ratio which is superior to that of hydrogen or helium by upwards of a factor of 10 - or less, with acceleration compression.
These come in various arrangements of plasma fuel composition, frequency of electromagnetism, ionization techniques and heating techniques - generally breaking down into pre-effect (heated by a reactor system, often fusion, a matter/antimatter reaction or even monopole-induced baryonic decay of matter itself) or post-effect (conventional thrust heated by radiowaves to ionize propellant as an extra stage to another type of engine).
Some types do not expel a complete 'thrust' of plasma itself but but instead just the ions coating its positive particles, which are provided using electrical charge: electricity goes in, ions (part of the electrical circuit of matter) come out, no propellant is expended. These are distinguished as ion engines and have a much lower thrust/weight ratio but are incredibly fuel efficient. These are ion engines.
To create plasma, a gas-like matter that’s as hot as the sun, radio waves are used to heat a gas propellant. The problem is that during the heating process, charged ion particles are expelled, causing damage to the thruster’s walls that could potentially lead to a catastrophe. These charged ions are very similar to ionizing gamma radiation coming from a nuclear blast that causes radiation sickness and other serious problems in people should the output of the engine be high enough.
Either the interior wall can be made of superior materials which are heavy and expensive or create a type of wall which can repair itself using a property called plasma re-deposition. While it isn't a permanent fix, it does mean an engine can be 'booted up' into re-deposition mode and matter be used to plug the gap in the engine's interior construction as it is added to the thrust-stream - and in turn, the lifetime of an engine can be extended dramatically.