The gas phase emitter effect at the anode in a high pressure sodium vapour discharge
T. Hartmann, Klaus Günther, Jürgen Mentel
Journal of Physics D: Applied Physics 43(2), volume 43, January 2010
To allow spectroscopic measurements within a high pressure sodium lamp, the translucent tube of the lamp is substituted by a transparent sapphire tube. Moreover, the sodium pressure in the lamp is adjusted by an external control of its cold spot temperature. The temperature distribution along the anode of a sodium dc discharge is determined pyrometrically with a special set-up for spectroscopic measurements in the near infrared in dependence on the arc current and the sodium vapour pressure. The power input from the arc plasma into the anode was determined by comparison with temperature distributions obtained by numerical simulation. A physical analysis of the power input yields a lowering of the work function of the tungsten anode to 2.6 eV in accordance with the reduced work function, which was found for the cathode of the sodium lamp.