2018 BFY III Abstract Detail Page
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||W09: Paschen’s Law Experiment
||For this experiment, participants will first study the DC glow discharge setup: a simple plasma source that is understandable to undergraduate students yet flexible enough to be used in a variety of experiments . This type of source is relevant to fluorescent lighting, plasma televisions, and surface treatment of materials. The DC glow discharge is composed of two conductors separated by some distance and electrical potential inside an evacuated vessel at moderately low pressures (between a few and a hundred Pascals). The electrical potential needs to be high enough (hundreds to thousands of Volts) to break down the gas into a plasma. The characteristics of the plasma are controlled by four variables: potential difference and distance between the electrodes as well as the type of gas used and its pressure. In our device, we evacuate glass vessels that house stainless steel electrodes. Each has a two-stage direct-drive vacuum pump, an inlet valve system, and a pressure sensor. While the vessels can be filled with any gas through one fine and one coarse valve, for this workshop we will study atmospheric air (mostly nitrogen and oxygen). These valves also enable fine control of the gas pressure from 3 to 300 Pa. We use power supplies that provide a potential difference of up to 2000 V and 20 mA.
Participants will investigate the transition from a gas to a plasma and correlate the breakdown voltage to the length of the tube and the gas pressure (Paschen's Law). We compare our experimental measurements to the ideal curve and use that to discuss sources of error in this multivariable system.
 S. A. Wissel, A. Zwicker, J. Ross, S. Gershman, "The Use of DC Glow Discharges as Undergraduate Educational Tools" AJP 81 , 663 (2013)
Princeton Plasma Physics Laboratory
100 Stellarator Road
Princeton, NJ 08540
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