Emissive Langmuir probes in the strong emission regime for the determination of the plasma properties

• Published in: 2012 Abstracts IEEE International Conference on Plasma Science p. 1A-1
• Main Authors: Tierno, S.P., Domenech, J.L., Donoso, J.M., Conde, L., Jennewein, D., Herdrich, G.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.07.2012
• Subjects: Electric potential; Plasma temperature; Probes; Sociology; Statistics; Temperature measurement
• ISBN: 9781457721274; 1457721279
• ISSN: 0730-9244; 2576-7208
• DOI: 10.1109/PLASMA.2012.6383291

The emissive Langmuir probes are made up of thin metallic wires exposed to the plasma and heated up to the electron thermoionic emission by a DC current 1,2,3 . They are essentially used to determine the local plasma potential V sp 1,2,3 and the electron temperature T e 4 . The weak and strong electron operation emission regimes of the probe are determined by means of the probe temperature T w . For probe bias voltages V p < V sp the experimental evidence points out that a fraction of the emitted electron population returns to the probe after colliding. The probe temperature dependent voltage current curves were found in agreement with a simple model, which accounts for this returned electron current. Therefore for low positive probe polarization voltages V p ⌷V sp two electron populations also coexist close to the probe; the electrons from the plasma and also the local emitted electrons of temperature TW that slightly alter the local potential around the probe. Thus, the electron saturation current results from the sum of two drained electron currents, and one of them relies on the wire temperature. The determination of the plasma potential and the electron temperature for polarization potentials V p < V sp by using the floating potential of the probe is also investigated. The plasma potential was obtained from the measurements of the floating potential as a function of the probe temperature. A sharp transition between two different regimes is observed at the temperature where floating potential equals the plasma potential. However, while on theoretical grounds the determination of the electron temperature T e is also possible 4 , the results obtained when using emissive and collecting probes differ. The different electron populations close to the probe when V p < V sp would be responsible of this disparity between the experimental results found with both probes.