Investigation Of Plasma Properties Research Articles

Investigation of plasma properties in the phase of the radial expansion of a spark channel in the ‘pin-to-plate’ geometry

Observations of the early stage of a spark discharge in air at atmospheric pressure in the pin-to-plate geometry under a single high-voltage pulse, including an initial stage of the channel expansion, are presented. It was shown that an interelectrode gap is closed by a large number of microchannels at 20–30 ns. The start of a radial channel expansion begins at the moment when the electron concentration reaches the maximum value of 2 × 1019 cm−3. Theoretical analysis based on the proposed model takes the following plasma-channel properties: electric field strength is about several kV cm−1, electron temperature is close to 2–3 eV, plasma conductivity is in the order of ∼200 Ω−1·cm−1, speed of the radial spark channel expansion is ∼5 km s−1.

Single filament charge transfer and UV-emission properties of a cascaded dielectric barrier discharge (CDBD) set-up

We present a so-called cascaded dielectric barrier discharge (CDBD) set-up. Compared to standard single-gap discharge set-ups, the cascaded arrangement uses an additional UV-transparent dielectric to form two separated discharge gaps. These can interact electrically and by transmission of UV light. Investigation of plasma properties is done by emission spectroscopy and by measurement of the single filament charge transfer. Clear differences in CDBDs compared to single-gap discharge arrangements are demonstrated. The CDBD set-up shows a smaller single filament charge transfer if a UV-transparent dielectric is used and—for both gaps—we obtain a higher conversion efficiency in the UV range than for a single-gap discharge.

The Role of Atomic Spectroscopy in Fusion Research

One of the problems encountered in thermonuclear fusion research deals with the presence of elements other than hydrogen isotopes in the plasmas created for these studies, and the effects of such impurities on plasma behaviour. As a result, atomic physics has played an important role in the investigation of plasma properties and behaviour ever since the early days of fusion research.With the tokamak device as an example, we will review some characteristic features of the spectra arising in such plasmas, and how the emitted lines may be used for localized plasma diagnostics. Some specific examples of diagnostic applications will be given.

Plasma Diagnostics and Energy Transport of a dc Discharge Used for Sputtering

An investigation of plasma properties and energy-transport mechanisms within a dc anomalous glow discharge has been conducted, with particular reference to those processes operating in the vicinity of the anode. The objective of this work was to obtain more quantitative information about the species in the plasma contributing to the heating of substrates located on the anode during sputtering. Techniques employed in this study involved the use of Langmuir probes for the detection of low-energy species, of an electrostatic analyzer for detection of high-energy species within the plasma, and of temperature-sensitive probes for energy-flux measurements. The negative glow of the plasma was found to contain two electron-energy distributions, one of density ∼2×1010 cm−3 and mean energy ∼0.6 eV, and the other ∼2×108 cm−3 and ∼6 eV energy. A low-energy positive-ion population approximately balanced these densities. Under all operating conditions, the plasma potential was found to be a few volts positive with respect to ground. Energy-flux measurements at the anode showed that the main source of energy was not from these populations in the plasma, however. Further examination of the discharge, using the electrostatic analyzer, revealed the presence of high-energy secondary electrons emitted at, or in, the vicinity of the cathode. Many of these electrons penetrated to the anode with the full fall of cathode potential, and it was found that they were the cause of the initial rapid rise of substrate temperature on commencement of sputtering. Radiation from uncooled cathodes was also a source of energy at the anode, once equilibrium temperatures had been approached.