Hagop Tawidian

Electron Temperature Evolution in a Low-Pressure Dusty RF Nitrogen-Rich Methane Plasma

Particles are generated in a classical planar RF (13.56-MHz) reactor in nitrogen-rich methane at low pressure (120 Pa). The gas decomposition leads to particle generation and growth. During their formation, the particles become negatively charged. The electrical and the optical parameters of the discharge are disturbed. The presence of particles in the plasma is put in evidence by laser light scattering and is correlated to the DC self-bias voltage. A small quantity of argon is introduced in the gas mixture in order to estimate the electron temperature. The temporal evolutions of both the electron temperature and the optical emission intensities of excited argon are correlated with the particle growth and behavior in the plasma.

Zoom Into Dusty Plasma Instabilities

In a krypton plasma, the growth of dust particles can strongly affect the plasma characteristics by inducing many types of instabilities. These unstable phenomena are studied by analyzing their frequency evolution as a function of time and by emphasizing the appearance of plasma spheroids. Different phases are evidenced due to a detailed analysis of the form and the frequency of the discharge current. Concerning the plasma spheroids, interesting motions in the plasma bulk are evidenced.

Characterization of low frequency instabilities in a Krypton dusty plasma

The occurrence of low frequency instabilities in a plasma can be due to the presence of a high density of grown dust particles. These instabilities are characterized by analyzing the discharge current, evidencing the existence of successive phases marked by distinct frequency evolutions. The main characteristics of these phases are determined as a function of the gas pressure. Particular attention is paid to the changes of the instability appearance time, duration and frequencies. These parameters seem to be related to global amount of grown dust particles. The instability appearance time is the first parameter that can be easily measured during an experiment and all the other parameters can be estimated from this simple measurement.

Unstable Plasmoids in Dusty Plasma Experiments

Low-frequency instabilities are easily obtained in dusty plasmas formed using reactive gases or material sputtering. These unstable phenomena can be characterized by complex and impressive features affecting the plasma glow luminosity. In this paper, we report on a particular phase of an instability, where moving bright plasma spots are observed in between the electrodes of a capacitively coupled radio-frequency discharge in krypton. These plasmoids show complex behaviors, such as mutual interactions, consisting in their merging or splitting.

High‐Speed Imaging of Dusty Plasma Instabilities

Dust particles in a plasma acquire negative charges by capturing electrons. If the dust particle density is high, a huge loss of free electrons can trigger unstable behaviors in the plasma. Several types of plasma behaviors are analyzed thanks to a high‐speed camera like dust particle growth instabilities (DPGI) and a new phenomenon called plasma spheroids. These small plasma spheroids are about a few mm, have a slightly enhanced luminosity, and are observed in the vicinity of the electrodes. Different behaviors are identified for these spheroids like a rotational motion, or a chaotic regime (fast appearance and disappearance).

Dust Particle Growth in a Sputtering Discharge with Krypton

Dust particles are grown in the PKE chamber by sputtering materials. The sputtering efficiency and the gas phase reactions can be affected by the gas type and particularly by the ion mass. Due to the presence of growing dust particles, the huge loss of electrons can trigger many instabilities in the plasma. These instabilities, the growth kinetics and the structure of the dust cloud, are compared by using two different gases: argon and krypton.