Mathematics – Logic
Scientific paper
Nov 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005phdt.........7p&link_type=abstract
Ph.D dissertation, 2005. 141 pages; Netherlands: Technische Universiteit Eindhoven (The Netherlands); 2005. Publication Number:
Mathematics
Logic
2
Sheath Phenomena, Dusty Plasmas
Scientific paper
In dusty plasmas, a void is called a dust-free region in the dust cloud levitated in the plasma. Voids have been observed both in the bulk plasma and in the plasma sheath. Part of this thesis investigates 2 D -voids developing in a dust cloud of 9.8m m -diameter particles levitating in the plasma sheath. The void size is found to increase with both power and pressure. The effect of the size of the trapping depression is also investigated. For our experimental conditions, no voids are observed above a small diameter (1 cm ) depression. The cloud-volume dependence on pressure and power is addressed by a phenomenological model. It fits well the trend in the void development with pressure and power.
The second phenomenon discussed here is orbital motion of individual particles trapped in the plasma sheath. As these particles are positioned below the main dust cloud of spherical particles, it is assumed that these particles are non- spherical coagulates. Their velocities increase with pressure and power. Some of the orbiting particles are also spinning. The observed orbiting has been compared to other experiments, in which similar effects have been induced, and it is proven that the mechanism of the orbiting in the actual experiment is different from the proposed mechanisms in the literature. It is shown that a symmetric particle can not perform orbiting motion.
The third new phenomenon described and explained in this thesis is counter- phase oscillations of particles with different size. By modulating the electrode voltage, particle oscillations are investigated. Two different sized particles are used: 4.8m m and 9.8m m . The particles oscillate in counter phase. Furthermore, a position where particles are not affected by the modulating electrical field has been found. This is corroborated by model results, showing that there is a position in the sheath where the electrical field is constant with changing plasma power. The particles levitated below this level move upwards with increasing plasma power, while those trapped above this level move downwards.
Based on the work performed in this thesis, we can conclude that the ion drag force on particles in the plasma sheath is negligible for phenomena occurring in the vertical direction, in which also the large gravitational and electrical forces act, but it is responsible for some interesting phenomena in the horizontal direction. (Abstract shortened by UMI.)
Paeva Gabriela Veselinova
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