Ionization and mobile charges
When electrons separate from neutral atoms, free electrons and positive ions appear. Under suitable conditions their electromagnetic interactions produce plasma behaviour. Neutral particles may remain, and ionization fraction is an important property, so plasmas do not all require every atom in a sample to be fully stripped.
References: [1]
Collective behaviour and instabilities
Electrons and ions respond differently to fields, while the fields they generate affect other particles. Waves and instabilities emerge from this collective behaviour. Experiments must therefore consider coupled motion, applied fields and boundaries rather than describe the system solely as a collection of independent collisions.
High- and low-temperature plasmas
Stellar interiors and fusion research involve high-temperature plasmas, while partially ionized low-temperature systems also exist. Conditions and particle energy distributions vary substantially. Describing every plasma simply as an extremely hot gas overlooks the different regimes studied in laboratories and exploited in manufacturing technologies.
References: [1]
Fusion research and manufacturing
Fusion systems investigate heating, confinement and control so suitable nuclei can react. Other applications use plasmas in surface processing and semiconductor manufacturing. They share the physics of ionized matter while differing in scale, energy and control objectives, requiring experimental parameters suited to the particular process.