Berlin 2001 – scientific programme

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P: Plasmaphysik

P 8: Magnetic Confinement and Plasma Technology (Poster Session)

P 8.23: Poster

Monday, April 2, 2001, 12:30–15:00, AT2

In situ Measurements to Determine the Effective Work Function — •Lars Dabringhausen, Daniel Nandelstädt, and Jürgen Mentel — Ruhr University of Bochum, Fundamentals of Electrical Engineering Group, Universitätsstr. 150, 44780 Bochum, Germany

The main task of a cathode in high intensity discharge (HID-)lamps is to emit electrons thermionically. The thermionic emission process is strongly affected by the cathode work function, which can vary during lamp operation. To determine the effective work function, precise measurements have been carried out on a special model lamp.

In particular, spatially resolved measurements of the cathode surface temperature have been performed using a single-wavelength pyrometer. Essential terms of the cathode power balance and the ion current fraction can be obtained using these measurements. In combination with the estimated size of the current transfer zone, the work function can be evaluated by applying Richardson’s equation to cathodes of different temperatures. Reasonable results were found. The enclosed iterative calculations show robust convergence for arbitrary initial guess values.

Financial support supplied by the German Federal Ministry of Education and Research, Ref.-No. 13N7763