Nonthermal plasma

A nonthermal plasma is in general any plasma which is not in thermodynamic equilibrium, either because the ion temperature is different from the electron temperature, or because the velocity distribution of one of the species does not follow a Maxwell-Boltzmann distribution.

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In the context of food processing, a nonthermal plasma (NTP) is specifically an antimicrobial treatment being investigated for application to fruits, vegetables and other foods with fragile surfaces. These foods are either not adequately sanitized or are otherwise unsuitable for treatment with chemicals, heat or other conventional food processing tools. The term cold plasma has been recently used as a convenient descriptor to distinguish the one-atmosphere, near room temperature plasma discharges from other plasmas, operating at hundreds or thousands of degrees above ambient (see here for more on plasma temperatures). In practical use, however, within the context of food processing the term "cold" can engender misleading images of refrigeration requirements as a part of the plasma treatment.

The nomenclature for nonthermal plasma found in the scientific literature is varied. In some cases, the plasma is referred to by the specific technology used to generate it ("gliding arc", "plasma needle", "plasma jet", "resistive barrier discharge", etc.), while other names are more generally descriptive, based on the characteristics of the plasma generated ("one atmosphere uniform glow discharge plasma", "atmospheric plasma", "ambient pressure nonthermal discharges", "non-equilibrium atmospheric pressure plasmas", etc.). The two features which distinguish NTP from other mature, industrially applied plasma technologies, is that they are 1) nonthermal and 2) operate at or near atmospheric pressure.

References

• Decontamination of Fresh Produce with Cold Plasma. U.S. Department of Agriculture. Retrieved on 2006-07-28.