Mitigating plasma constriction using dielectric barriers in radio-frequency atmospheric pressure glow discharges

Abstract

It is known that radio-frequency (rf) atmospheric glow discharges with bare electrodes are susceptible to plasma constriction at large discharge currents. This is undesirable for large-scale applications, even though large currents usually lead to abundant plasma reactive species and high application efficiency. In this letter, an experimental investigation is presented to demonstrate that plasma constriction can be mitigated by introducing dielectric barriers to the electrodes. The resulting atmospheric rf dielectric-barrier discharge is shown to operate in the γ mode of large discharge current while maintaining its discharge volume. This improves significantly plasma stability and the application potential.

Mode transition in radio-frequency atmospheric argon discharges with and without dielectric barriers

“…The larger breakdown voltage of the rf DBD is a result of its two dielectric barriers dividing into the applied voltage. 11 For both atmospheric argon discharges, the applied voltage undergoes a large reduction of more than 660 V immediately after the breakdown, distinctly different from rf glow discharges in atmospheric helium. 10,11 Subsequently, the Ar rf APGD evolved directly into a constricted plasma column of about 1 mm in diameter at point B in Fig.…”

“…11 For both atmospheric argon discharges, the applied voltage undergoes a large reduction of more than 660 V immediately after the breakdown, distinctly different from rf glow discharges in atmospheric helium. 10,11 Subsequently, the Ar rf APGD evolved directly into a constricted plasma column of about 1 mm in diameter at point B in Fig. 1͑a͒ image not shown͒ and further increase in the input rf power was found to be incapable of evolving the constricted plasma into a large-volume homogenous discharge.…”

“…9 Recently, dielectric insulation of electrodes is also found beneficial. 10,11 By increasing the power input after gas breakdown, dielectrically insulated electrodes lead to largearea homogenous Ar APGD, whereas bare electrodes tend to evolve the argon discharge directly into constricted plasma. However, little is known of the underpinning physics.…”

Atmospheric glow discharges from the high-frequency to very high-frequency bands

“…It is known that with sufficient input power the sheath region could undergo an abrupt collapse thus causing the discharge to enter the less stable ␥ mode. [5][6][7][8][9] In the 20 MHz case, point a marks the ␣ − ␥ mode transition beyond which increasing input rf power was found to constrict the discharge into a bright plasma column typically less than 1 mm in diameter. In the 40 and 60 MHz cases, points b and c indicate plasma conditions under which the discharge became radially inhomogeneous, consisting of an optically intense channel surrounded by a weak but expansive and diffuse region.…”

“…Compared to low-pressure discharges, homogeneous APGDs are much more susceptible to rapid transition into a constricted ␥ mode when excited in the common high-frequency ͑HF͒ band of 3-30 MHz. [5][6][7][8][9] By reducing the input rf power, it is possible to operate in the more stable ␣ mode but at the expense of low electron densities thus compromising their application efficiency. 10 One technique to achieve high plasma density without plasma constriction is to add a dielectric barrier to the electrodes so as to control the growth of the discharge current.…”