1999
IEEE International Conference on Plasma Science,
Monterey, California, USA, June 20-24, 1999
(ISBN 0-7803-5224-6)
Two-temperature, two-dimensional modeling of cathode hot spot formation
including sheath effects - application to high pressure xenon arc lamps
J Wendelstorf, H Wohlfahrt und G Simon
[5P03, p.240, abstract published only:]
One of the fundamental problems in high pressure gas discharges is the
prediction of plasma/cathode interaction. The cathode hot spot temperature
determines electron emission and plasma formation. The critical physical
processes in the cathode/plasma system are electron emission, heat
conduction and the formation of the cathodic boundary layers and the
thermal plasma expansion zone. The nonlinear interaction of these
phenomena is decisive for important technological parameters like
electrode erosion and peak plasma temperature, e.g. in HID-lamps.
The self consistent single temperature model [1] is extended to allow for
deviations of electron temperature Te from heavy particles temperature Th.
Modeling of the cathode-plasma region now includes the following physical
processes self consistently:
- heat conduction within the cathode body (2-D).
- electron emission of the surface (T, TF,...).
- space charge layer formation (sheath).
- diffusion and ionizational non-equilibrium within a thin skin layer (presheath).
- current and heat transport in the cathodic plasma, without the LTE assumption (2-D).
Assuming a stationary discharge in cylindrical symmetry,
the model is applied to high pressure xenon short arc lamps
with operating pressures of 1-4 MPa and currents of several ampere.
The temperature split region is found to extend over 200µm in
front of the cathode surface. Sheath effects critically influence
the hot spot temperature of the cathode.
This modeling approach can be regarded as an important step in
the development of predictive models of thermal plasma gas
discharges like high pressure (arc) lamps.
Financial support by the BMBF (Germany)
under Contract No.13N7105 is gratefully acknowledged.
[1] J Wendelstorf et.al., 8th Int. Symposium Science & Techn. Light Sources (LS-8), Greifwald, 1998, M01, p.382
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