The mode transition induced by varying the low-frequency current in low-pressure dual-frequency discharges in argon is found through particle-in-cell or Monte Carlo simulations. As the low-frequency (2 MHz) current increases for the fixed high-frequency (27 MHz) current, the electron distribution function (EDF) changes from Druyvesteyn to bi-Maxwellian (in alpha mode) or Maxwellian-type (in gamma mode), along with the significant drop in the effective electron temperature. It is shown that this EDF evolution is attributed to the transition from collisional to collisionless property (but not stochastic heating) of the low-energy electrons as well as the alpha-gamma transition.

The application of nonthermal atmospheric pressure plasma to intracoronal bleaching could be a novel and efficient therapy in the bleaching of haemorrhagically stained teeth.

No abstract

Collection of point-like intense vortices arranged symmetrically outside of a uniform circular vortex patch, both enclosed in a free-slip circular boundary, are numerically time evolved for up to 10–15 patch turnover times. These patterns are found to merge with the patch by successively inducing nonlinear dispersive modes (V-states) on the surface of the patch, draw off fingers of vorticity (filamentation), trap the irrotational regions as the fingers symmetrize under the shear flow of the patch and point-like vortices (wave breaking) followed by the vortex–hole capture. While the hole patterns are observed to break up over several turnover periods the vortex patterns appear to evolve into quasistationary patterns for some cases of an initial number of point-like vortices Npv. The bounded V-states, filamentation, and vortex (hole) pattern formation are discussed in some detail and their possible connection to recently observed vortex “crystals” is pointed out.

An internal-type linear inductive antenna, referred to as a “double comb-type antenna,” was used as a large area plasma source with a substrate size of 880×660mm2 (fourth generation glass size). The effects of the dual frequency (2 and 13.56MHz) radio frequency (rf) power to the antenna as well as the power ratio on the plasma characteristics were investigated. High-density plasma on the order of 1.7×1011cm−3 could be obtained with a dual frequency power of 5kW (13.56MHz) and 1kW (2MHz) at a pressure of 15mTorr Ar. This plasma density was lower than that obtained for the double comb-type antenna using a single frequency alone (5kW, 13.56MHz). However, the use of the dual frequency with a rf power ratio of approximately 1(2MHz):5(13.56MHz) showed better plasma uniformity than that obtained using the single frequency. Plasma uniformity of 6.1% could be obtained over the substrate area. Simulations using FL2L code confirmed the improvement in the plasma uniformity using the dual frequency to the double comb-type antenna.