Abstract-The presheath located near boundaries in weakly ionized plasmas is a rich environment in which charge exchange, and ion-ion streaming instabilities combine to establish the electric fields that accelerate ions to close to the Bohm velocity at the sheath/presheath boundary. Charge exchange sets the presheath scale length in weakly collisional plasma, in which ionization can be neglected. The transition of mobility limited ion flow near the bulk plasma to free fall motion close to the plate for single species plasmas is explored. Measurements in argon-helium multidipole plasmas of plasma potential with emissive probes and ion energy distribution functions with laser induced fluorescence are presented. These data show that the argon ions are speeded up by the presheath electric fields, argon ions are heated, and ion-ion instability is present as ions approach the boundary.Index Terms-Bohm velocity, charge exchange, free fall motion, ion-ion streaming instability, ion velocity, mobility limited flow, presheath, sheath, weakly ionized plasma.

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The concentration of two species in a multi-dipole plasma was determined by measuring the ion acoustic wave group velocity and the electron temperature. The wave was launched from a grid immersed in the plasma and was detected by a Langmuir probe. Electron temperature was found separately from an I–V characteristic trace. The measurements were performed in helium/xenon and argon/xenon plasmas. Typical parameters of the plasma were Te∼0.5–3 eV, density 1010 cm−3, plasma potential of 3–5 V, and pressure range from 1 to 20 mTorr. The accuracy of the measurement was from 2% to 4% depending on the mass difference between the two species and how accurately the group velocity and electron temperature are measured.

Packed bed dielectric barrier discharges (DBDs) are very promising for several applications including remediation of environmental pollutants and greenhouse gas conversion. In this work, we have investigated the space and time-resolved emission from a packed bed DBD operated in helium, to understand the plasma dynamics. We have chosen a simple planar DBD arrangement with a patterned dielectric, which mimics the spherical boundaries between the dielectric pellets and allows the optical access to the plasma. The results show that plasma is sustained in a packed bed DBD by three mechanisms: filamentary discharge in the void (between the center of dielectric structures and the opposite electrode), microdischarges at the contact points and surface ionization waves over the dielectric surface. It is observed that for most of the duration plasma is generated at the contact points between the dielectric structures.

Electrochromic (EC) properties of tungsten trioxide (WO 3 ) was improved with preparing hybrids of tungsten trioxide−titanium dioxide (WO 3 −TiO 2 ) and tungsten trioxide−poly(3,4-ethylenedioxythiophene) (WO 3 −PEDOT) by a rotating capacitively coupled radio frequency (rf 13.56 MHz) plasma reactor. Energy-dispersive X-ray spectroscopy mapping results indicated that TiO 2 and PEDOT were coated homogeneously onto the surface of the WO 3 powders. Thin films of hybrid powders have been prepared by the physical vapor deposition method of the electron beam evaporation technique. Redox potentials, optical contrast at 700 nm, and durability during 2000 cycles of EC devices were investigated, comparatively. Hybrids of WO 3 indicated excellent coloration efficiency (cm 2 C −1 ) and switching speed values compared with untreated WO 3 . The coloration efficiency values were found to be 85.88 and 41.61 cm 2 C −1 of WO 3 −TiO 2 and WO 3 −PEDOT, respectively. The switching speed of WO 3 (13.3 s, from bleached state to colored state) increased to 1.4 s for WO 3 −TiO 2 .