Observation of different modes of cathodic arc attachment to HID electrodes in a model lamp

Electrodes made of pure and doped tungsten are operated in a special model lamp with a DC current of 1-10 A in argon or xenon atmosphere within the pressure range of 0.1-1 MPa. Cylindrical electrodes with different designs are investigated with regard to the mode of cathodic arc attachment. Three modes are observed: a diffuse mode, a spot mode and a super-spot mode. The major difference between the diffuse and the spot mode is the current density, which is low in the case of the diffuse mode and high in the spot mode. The diffuse mode is favoured by high current, low pressure and weak cooling of the electrode, the spot mode by the opposite conditions. In a transition region the cathode changes statistically between these modes. Whereas the global electrode temperature and the cathode fall of the diffuse and the spot mode differ slightly, the super-spot mode is associated with a significantly decreased global electrode temperature and cathode fall at similar parameters. SEM pictures show that the surface structure of the electrodes has wide influence on the mode of cathodic arc attachment. Due to the significant difference between the super-spot mode and the two other modes this paper is concentrated on the comparison between the spot and the diffuse mode.

[1]  J. Waymouth.  Electric Discharge Lamps , 1971, Nature.

[2]  J. Mentel,et al.  Determination of HID electrode falls in a model lamp I: Pyrometric measurements , 2002 .

[3]  W. Bötticher,et al.  Numerical modelling of a dynamic mode change of arc attachment to cathodes of high-intensity discharge lamps , 2001 .

[4]  H Pursch,et al.  Arc attachment and fall voltage on the cathode of an ac high-pressure mercury discharge , 2002 .

[5]  A. Anders,et al.  On modes of arc cathode operation , 1991 .

[6]  H. Schmitz,et al.  Consistent analysis of the boundary layer of a Saha plasma , 2001 .

[7]  R Bötticher,et al.  Numerical modelling of arc attachment to cathodes of high-intensity discharge lamps , 2000 .

[8]  J. Mentel,et al.  Observation of an extremely constricted cathodic arc attachment to electrodes of high intensity discharge lamps , 2002 .

[9]  J. Waymouth.  Analysis of cathode-spot behavior in high-pressure discharge lamps , 1982 .

[10]  H. Schmitz,et al.  Analysis of the cathodic region of atmospheric pressure discharges , 2002 .

[11]  M. Benilov,et al.  A model of the cathode region of atmospheric pressure arcs , 1995 .

[12]  W. Weizel,et al.  Lichtbögen mit und ohne Brennfleck , 1952 .

[13]  W. Haidinger.  Ein Beitrag zur Kenntnis der brennflecklosen Bogenentladung , 1958 .

[14]  J. Reiche,et al.  Diagnostics of discharge modes of a free-burning low-current argon arc , 2001 .

[15]  J. Mentel,et al.  Determination of HID electrode falls in a model lamp III: Results and comparison with theory , 2002 .

[16]  M. Neiger,et al.  A novel experimental method for in situ diagnostics of electrode workfunctions in high-pressure gas discharge lamps during operation , 2000 .

[17]  M. Neiger,et al.  Numerical simulation of dc high-pressure discharge lamps including electrodes , 2002 .

[18]  H. Maecker,et al.  Plasmaströmungen in Lichtbögen infolge eigenmagnetischer Kompression , 1955 .

[19]  J. Meunier,et al.  Thermo-field emission: a comparative study , 1997 .

[20]  R. Rompe,et al.  Ergebnisse der Plasmaphysik und der Gaselektronik , 1967 .

[21]  E. Pfender,et al.  Measurement of anode falls and anode heat transfer in atmospheric pressure high intensity arcs , 1984 .