|Title:||Investigations on high pressure direct current glow-discharges||Language:||English||Authors:||Maszl, Christian||Qualification level:||Diploma||Keywords:||Gleichstrom Glimmentladung; Ähnlichkeitsgesetze; Paschen-Kurven; Durchmesser positive Säule; reduzierte normale Stromdichten; Temperatur Kathodenfall; Anodenlichtpunkte; selbstorganisierte Strukturen; reduzierte Feldstärken; Helium
direct current glow-discharge; similarity laws; paschen curves; positive column cross section; reduced normal current density; temperature cathode fall; anode light spots; self-organized structures; reduced field strength; helium
|Advisor:||Laimer, Johann||Issue Date:||2008||Number of Pages:||200||Qualification level:||Diploma||Abstract:||
Direct current (DC) glow-discharges are well known today and in widespread use. However, there is less known about DC glow-discharges at high pressures. High pressure glow-discharges are interesting because expensive and maintenance-intensive vacuum equipment is not required. This fact allows minituarization of discharges for various applications. Main goal of this study was to investigate similarity ("scaling") laws for high pressure DC glow-discharges. Therefore, a high pressure chamber was constructed in order to observe glow discharges in a pressure range from 200 to 2000 hPa with inter-electrode gaps between 0.1 and 7 mm. Distances are adjusted with a micrometer-head. Both electrodes are water cooled to allow measurements at higher powers. The electrodes are replaceable to permit experiments with various electrode materials. Electrical characterisation of the discharge is accomplished by the determination of current-voltage (I-V) curves. Optical analyses are done with microscopes and spectrometers. Investigations on breakdown voltages were performed. It turned out that neither of the established formulas for the ignition potential is capable to fit the experimental data. The reduced normal current density for helium and copper was measured for the first time. Investigations on the pressure dependence of the positive column cross section and the temperature in the cathode fall region took place. I-V characterisation and measurements of the reduced field strength in the positive column of mathematically similar discharges were performed. The reduced thickness of a normal cathode sheath was measured for the first time for helium and tungsten. Finally, investigations on anode light spots and anode glows took place. Two different types of anode spots, ring-like structures and self-organised hexagonal structures were observed. Violations of the similarity laws are presented and the influence of gas heating on the discharge parameters in the high pressure case is demonstrated. Glow-discharges with operating voltages below the normal cathode fall voltage are presented. This work provides a broad overview of a variety of phenomena and a solid base for future research.
|Library ID:||AC05036703||Organisation:||E134 - Institut für Allgemeine Physik||Publication Type:||Thesis
|Appears in Collections:||Thesis|
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checked on Feb 18, 2021
checked on Feb 18, 2021
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