Plasma afterglow

A plasma afterglow (also afterglow) is the radiation emitted from a plasma after the source of ionization is removed. The external electromagnetic fields that sustained the plasma glow are absent or insufficient to maintain the discharge in the afterglow. A plasma afterglow can either be a temporal, due to an interrupted (pulsed) plasma source, or spatial, due to a distant plasma source. In the afterglow, plasma-generated species de-excite and participate in secondary chemical reactions that tend to form stable species. Depending on the gas composition, super-elastic collisions may continue to sustain the plasma in the afterglow for a while by releasing the energy stored in rovibronic degrees of freedom of the atoms and molecules of the plasma. Especially in molecular gases, the plasma chemistry in the afterglow is significantly different from the plasma glow. The afterglow of a plasma is still a plasma and as thus retains most of the properties of a plasma.

The first published pictures of plasma afterglow were taken in 1953.

Helium afterglow, one of the most commonly used forms of afterglow, was first described in 1963 by Arthur L. Schmeltekopf Jr. and H. P. Broida.

The first flowing afterglow ionization studies began in the early 1960s in an effort to understand atmospheric ion chemistry. At the time stationary afterglow studies had already been done however this approach was limited by lack of versatility and lacked consistency as studies done prior to 1964 showed common atmospheric reactions to have drastically differing reaction rates between studies. Flowing-afterglow was then used to more precisely describe the rate constants of common atmospheric reactions

A remote plasma refers to a plasma that is spatially separated from the external electromagnetic fields that initiate the discharge. An afterglow is a remote plasma if the plasma is channeled away from the original plasma source.

An advantage that remote plasma has over temporal plasma is that remote plasma can be used as a continuous plasma source and thus has more applications in supplying reagent ions for most systems.

Remote plasmas are often used used in the field of analytical chemistry when a constant stream of ions is required. They are also very commonly used a method of cleaning complex vacuum systems without having to take them apart.

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