Langmuir Probe

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Description of the Experiment

This experiment's purpose is the determination of the capacity of a variable coax cylindrical capacitor. It has two sections, a first with a Polystyrene dielectric, and a second with air, allowing the determination of the relative dielectric constant of Polystyrene.


  • Video: rtsp://
  • Laboratory: New Experiments in[1]
  • Control room: Langmuir Probe
  • Level: ****

Experimental Apparatus

The main chamber consists of a pirex cylinder on which a modified Filament Head is placed to function as a Langmuir probe.

The central filament of 0.2mm diameter has been covered with alumina tube leaving only a 1cm tip exposed to the plasma. The two outer filaments are connected to an "of the shelf" RF generator which ionizes the gas and generates the plasma. This is a simple 3.5W generator which outputs a 50kHz AC signal with 1kV amplitude. To improve stability and homogeneity of the electrical field two molybdenum plaques have been attached using low vapour pressure epoxy, to each outer filament.


Determination of the electron temperature and density