Atmospheric-pressure plasma

Atmospheric-pressure plasma (or AP plasma or normal pressure plasma) is a plasma in which the pressure approximately matches that of the surrounding atmosphere – the so-called normal pressure.

Atmospheric-pressure plasmas have prominent technical significance because in contrast with low-pressure plasma or high-pressure plasma no reaction vessel is needed to ensure the maintenance of a pressure level differing from atmospheric pressure. Accordingly, depending on the principle of generation, these plasmas can be employed directly in the production line. The need for cost-intensive chambers for producing a partial vacuum as used in low-pressure plasma technology is eliminated.

Various forms of excitation are distinguished:

Atmospheric-pressure plasmas that have attained any noteworthy industrial significance are those generated by DC excitation (electric arc), AC excitation (corona discharge, dielectric barrier discharge, piezoelectric direct discharge and plasma jets as well as 2.45 GHz microwave microplasma).

By means of a high-voltage discharge (5–15 kV, 10–100 kHz) a pulsed electric arc is generated. A process gas, usually oil-free compressed air flowing past this discharge section, is excited and converted to the plasma state. This plasma then passes through a jet head to arrive on the surface of the material to be treated. The jet head is at earth potential and in this way largely holds back potential-carrying parts of the plasma stream. In addition, it determines the geometry of the emergent beam.

Based on transistor amplifiers up to 200W power RF (radio frequency) and microwave sources are used to generate a microwave plasma. Most of the solutions work at 2.45 GHz. Meanwhile, is a technology developed which provide the ignition on the one hand and the high efficient operation on the other hand with the same electronic and couple network. This kind of atmospheric-pressure plasmas is different. The plasma is only top of the electrode. That is the reason the construction of a cannula jet was possible.

The plasma jet is used, among other things, in industry for activating and cleaning plastic and metal surfaces prior to adhesive bonding and painting processes. Even sheet materials having treatment widths of several meters can be treated today by aligning a large number of jets in a row. In doing so the modification of the surface achieved by plasma jets is comparable to the effects obtained with low-pressure plasma.

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Wikipedia