Plasma sources generate plasmas.

Excitation of a plasma requires partial ionisation of neutral atoms and/or molecules of a medium. There are several ways to cause ionisation: collisions of energetic particles, strong electric fields acting on bond electrons, or ionising radiation. The kinetic energy for ionising collisions may come from the heat of chemical or nuclear reactions of the medium, as in flames, for instance. Alternatively, already released charged particles may be accelerated by electric fields, generated electromagnetically or by radiation fields. If at least as many charge carriers are created per time unit as recombine, the plasma can be sustained.

Plasma excitation by electromagnetic fields can be classified according to:

• Frequency classification of plasmas
• Energy coupling mode
  • Inductively coupled plasma
    • Solenoid coil
    • Planar coil
    • Helical resonator
  • Capacitively coupled plasma
    • Parallel plate recator
  • Wave-heated plasma
    • Electron cyclotron resonance
    • Helicon discharge
    • Surface-wave-sustained mode
    • Resonator mode
  • Electrode-less plasma excitation
• Pressure range classification
  • Low pressure discharge
  • Atmospheric pressure discharge

Plasma sources have numerous technical applications, for instance in light generation and plasma processing of materials.