Background

Plasma - a distinct phase of matter, considered as the 4th state. It is a collection of charged particles that respond to electromagnetic fields. Since the particles in plasma are electrically charged (generally by being stripped of electrons) it is frequently described as ionized gas.

• Plasma was identified by Sir Williams Crookes in 1879.
• Plasma's nature of matter was identified in 1897.
• The term "plasma" was assigned by Irving Langmuir in 1928.
• Examples of plasma: flame, lightning, nebulae, stars, the empty vastness of space etc.

Low-pressure plasma discharges:

• Glow discharge - non-thermal plasma generated by the application of DC or low frequency (RF below 100KHz) electric field to the gap between two metal electrodes.
• Capacitively Coupled Plasma - generated with high frequency RF electric fields. typically 13.56 MHz. The sheaths are much less intense than the glow discharge.

Atmospheric pressure plasma discharges:

• Dielectric Barrier Discharge (DBD) - non-thermal discharge generated by the application of high voltages across small gaps wherein a non-conducting coating prevents the transition of the plasma discharge into an arc. 
• Capacitive Discharge - non-thermal plasma generated by the application of RF power to one powered electrode with a grounded electrode held at a small separation distance around 1 cm. Usually helium or argon are used.